520 AGRICULTURAL REPORT.

OBSERVATIONS ON ATMOSPHERIC HUMIDITY.

BY J. S. LIPPINCOTT, HADDONFIELD, N. J.

To a large and intelligent class of readers of the Agricultural Department reports, grape-growing has become an object of absorbing interest. Those of this class who may have read a paper on “The Climatology of American Grape Vines,” in the report for 1862, and its continuation under the title of “Geography of Plants,” in that for 1863, will have observed that success was promised in certain zones of summer temperature, provided the atmospheric humidity were not there deficient, either permanently or for the season. This element, 80 variable, seems scarcely less important than that of the mean temperature of the growing season. Experience derived from the failure of the grape crop of 1864 and 1865, over wide regions deficient in humidity, and its success in others where this element must have been abundant, have set its value in a clearer light than heretofore.

In seasons not marked by extreme fluctuations of atmospheric humidity, and accompanying reductions of temperature in midsummer, the isotherms which bound the. grape-growing belts, as heretofore described, limiting the regions adapted to certain varieties of grapes, may still be esteemed as normally correct and reliable; but in seasons of exceptional character, when extremes of humidity occur, and, with them, extreme high temperatures followed by great reduction of atmospheric moisture, (and oftentimes accompanying sudden decline during the-night to near the freezing point,) such isotherms cease to. be the guiding clews to the regions adapted to any special variety of grape, or, indeed, to indicate that any grape can be. therein successfully cultivated, There are few physical laws which can be realized with mathematical exactness, but they are generally approximations, more or less false, in each particular case. “These laws are ideal truths towards which nature tends, but which are never fully reached. Even as respects the law of gravitation, there always have been residual phenomena unexplained by the law; and so, probably, there always will be as our generalizations widen towards the great Presence of which all natural phenomena are the direct manifestation.”

We have hitherto regarded the conditions of temperature as of primary importance. Though the amount of moisture in the atmosphere of each locality may be of nearly equal value, we have not the data for determining the proportions of this ingredient demanded for the successful culture of many of our garden and field products.

With regard to the grape, we are better prepared to discuss the question of the climatic value of excessive or diminished relative humidity. The very favorable reception awarded our former efforts, encourages the hope that the present will prove suggestive, if not instructive.

As a necessary. consequence of the evaporation continually going on over the entire surface of the earth, the atmosphere at all times contains a proportion of vapor of water, the amount of which is perpetually varying, This amount is almost.always below the proportion which experiment has shown to be the greatest degree possible at the observed temperature. It is owing to this circumstance that the air is rarely fully charged with vapor—that wet bodies become dry, and that the surface of the soil, although saturated with moisture, yet in a few hours becomes parched and dusty. By the process of evaporation from the surface of the land, as well as of the ocean, a natural distillation is thus continually carried on, and a perpetual circulation of waters maintained—those conveyed by the rivers into the sea being returned by invisible channels through the atmosphere to form clouds, which shall restore to the streams, by means of rain, their perpetual tribute to the ocean.

Upon variations in the quantity of moisture present in the atmosphere, many of the great peculiarities of our climate mainly depend. The frequency of rain, and many other meteorological phenomena of the highest interest and importance, are greatly; influenced by the proportions of humidity present in the atmosphere of any locality. To attain an accurate knowledge of the quantity of aqueous vapor which exists at any given time in a certain bulk of air, becomes, therefore, a problem which is constantly requiring solution. Instruments employed for this purpose are termed hygrometers. Various methods have been devised for ascertaining the proportion of moisture in the air; and the simplest and the most accurate of these consists in the determination of the dew-point, or temperature to which the air must be reduced so that its moisture shall begin to separate and condense upon cold surfaces. This difference, alone, is sometimes used to express the dryness of the air, or the reduction of its moisture below the point of saturation. The determination of the dew-point may be readily made, on a summer’s day, by noting with a delicate thermometer the exact temperature of water in a glass, at the moment deposition of vapor ceases to be made. From this temperature, and that of the air at the same time, the tension (pressure, or force) of the aqueous vapor present in the air, as exerted on the column of mercury in a barometer, may, by means of tables constructed for this purpose, be readily ascertained; and the corresponding proportion of moisture (or the relative humidity or percentage of saturation) be easily learned.

The above method, apparently so simple, is uot readily employed in general practice, and has given place to the wet-bulb thermometer, or August’s Psychrometer, which for simplicity and ease of manipulation leaves nothing to be desired. This consists merely of two similar delicate accurate thermometers, placed side by side on the same stand, the bulb of one covered with thin muslin, which is supplied with moisture and kept continually wet by capillary conduction from a vessel beneath. The action of this instrument may be readily understood by the uninitiated observer, who, with one hand wet and the other dry, will expose them equally to a gentle current of air, on a drying day. He will not need a thermometer to indicate which hand is most rapidly cooled, and that the drier the day, the more his wet hand will become chilled below the other.  Thus it is with the “wet and dry bulb” thermometers. The wet bulb thermometer will exhibit decline in temperature if the air be not already saturated with moisture, and evaporation thereby prevented. The rate of evaporation, and consequently the depression of temperature in the wet-bulb instrument, will be greater in proportion as the air is further from the point of saturation. To determine the exact amount of vapor present, and the proportional degree or percentage of saturation, tables have been prepared which greatly facilitate the study of hygrometry; the best of which are those published by the Smithsonian Institution, at Washington. Without such tables, the indications of the Psychrometer, except when very near saturation, can be but vaguely defined, since the amount of vapor contained in the air, at any time, is reduced by a fall in temperature, more rapidly than in direct proportion to the fall; for while the temperature changes in arithmetical, the humidity varies in geometrical progression. It should be understood that the amount of vapor held in the air over any district is very variable—perhaps constantly changing in amount. The ‘colder the air, the less the vapor it can hold; and the warmer the air, the more it may contain. But it does not follow that there must necessarily always be more vapor in the air at a high temperature than at a lowerone. Air at a given temperature will hold a certain quantity of vapor, and no more; but it may hold any quantity less. If heated, it may absorb more, (if not already full or saturated,) if it can gain access to it, or to water.  If already full, it will lose a part of it on being chilled. The definite quantities of vapor which air will hold at certain temperatures, by Fahrenheit’s thermometer, are as follows: At zero the weight of vapor ina cubic foot of saturated air has been estimated at about three-quarters of a grain ; at 32°, 24 grains; at 40°, 3 grains; at 50°, 4} grains; at 60°, 57 prains ; at 70°, 8 grains ; at 80°, nearly 11 grains; at 90°, 144 grains; at 95°, 17 grains, and at 160°, nearly 20 grains of vapor in each cubic foot.

When an atmosphere of very high temperature is loaded with all the vapor it can hold, as at 95°, saturated with 17 grains for every cubic foot, it becomes very oppressive to the people of the district sustaining it, and sometimes destructive to life. A consideration of the above numbers will explain the general extreme humidity of the climates of warm countries. The amount of vapor in the air is not generally expressed in grains in each cubic foot, but in inches of pressure on the barometer, and in degrees of relative humidity, 100 being taken to represent saturation. This ever fluctuating element varies from hour to hour through each day, according to the changing temperature of the air, the action of the sun’s rays, the presence or absence of clouds, and the force of the wind.  It may be reduced almost, if not quite, to a nullity, or may rise at high temperatures until it presses upon the barometer with a force measured by two inches of its column. Throughout the year it is generally least or lowest in the morning about sunrise, when a portion has been deposited as dew or frost ; and greatest or highest at 24 p. m., or about the period of greatest heat; and declines again in the evening, but not to the low measure of the morning. These are the mean average conditions, but it may be, and it often is, greatest in the morning, lowest at noon, and lower in the evening than at the morning observation. It is at its lowest point, generally, in January, when we have observed about one hundredth of an inch; increases in February, and advances in quantity as the season progresses, until it reaches its greatest amount in August, during the periods of greatest heats; then declines with the decline of heat, the humidity of autumn being in advance of that of spring. The highest we have observed the pressure of vapor was on the 7th of July, 1864, when it affected the barometer to the extent of 1.235 inch, the thermometer being at 90° at 2 p.m., and on the 26th of June, 1864, 1.053 inch at 2 p. m., thermometer at 96°, both of which were followed by rain in one to three hours—the last with lightning and tornado blasts of wind.

A general idea of the comparative mean force of vapor in the air near Philadelphia may be gained from the following table of the results of reductions for two years past:
Force of vaporIn inchesForce of vaporIn inchesForce of vapor in 1864-'65
LowestHighestRange
1864―March.1671865―March.219.05.280.230
April.237April.285.115.440.325
May.438May.399.189.857.668
Mean for spring.280Mean for spring.301
1864—June.4721865—June.667.2131.053.840
July.543July.671.2761.235.959
August.659August.687.327.856.529
Mean for summer.558Mean for summer.675
1864—September.4621865—September.646.255.744.489
October.306October.332.168.723.555
November.253November.242.103.537.434
Mean for Autumn.340Mean for autumn.405
1864―December.1701865—December.194.059.407.348
1865—January.1101866—January.133.021.376.355
February.1421866—February.043.349.306
Mean for winter 1864-'5.105Mean for winter 1865-'6.163
Mean for year.327Mean for the year.386

By the above table it will be seen that the mean pressures of vapor for the spring of 1864 and 1865 were nearly identical ; that for the dry summer of 1864 much less than that of 1865, which was not in this region so marked by drought; that of September, 1865, greatly in excess of that of 1864, as will be remembered by many who suffered from the oppressive dampness, and by those whose grapes were destroyed by rot in that month; that the mean for autumn, 1865, was therefore greater than for the previous year, and, finally, that the past winter has also been more moist than its predecessor, and for the entire year rather greater than that of 1864; all of which is in perfect accordance with our general impressions from empirical observation.

The absolute amount of vapor present in the air, as measured by the barometer, does not express the dryness or humidity as generally affecting our feelings, or the health of vegetation, but it is the evaporating power of the air which it most concerns us to know, or its capacity to take up more vapor at the temperature observed, and to deposit a portion, or become saturated, by a loss of heat. High heats with abundant moisture, (or high relative humidity,) are favorable to some crops at certain seasons, though injurious at others. High heat and dryness are as unfavorable to some as they are beneficial to others. In June, 1864, were observed many days of low humidity with low mean temperatures, followed by high heats with greater dryness. These proved injurious to the wheat in this region, ripening it too rapidly, drying its stem and berry before it had swelled, and preventing the elements necessary to its perfect development from reaching the grain in the gradual and timely manner needed for its perfect maturation. In June, 1865, were many days of moderate heat, none excessive, (though the mean was very high from the uniform greater heat than ordinary,) equalling the greatest mean for July, but accompanied by unusual relative-humidity, (more than 40 per cent. in advance of that of June, 1864,) and the wheat crop was again injured, while the corn made a growth so extraordinary that it was the subject of frequent remark, as exceeding anything remembered. The exceeding low relative-humidity of June, 1864, and of August, 1865, and the excessive moisture in September, 1865, of which we shall have occasion to speak, are instances of the vast utility of the presence of a due proportion of this element. By the term “relative-humidity,” is intended to express the amount of moisture existing in the air, compared with that which it could hold if saturated at the same temperature. A clear comprehension of the meaning of the terms, “tension,” “force,” or “pressure of vapor,” as measured by the barometer, and of relative-humidity, as expressive of the percentage of saturation, are necessary to an understanding of the subject under discussion. Moreover, it must be remembered that the dryness expressed by the difference between the temperature of the air and the dew-point is not to be confounded with the dryness, as expressed by the percentage of saturation. The former method is not now employed, having given place to the latter more philosophical mode of expressing relative dryness or humidity. The dew-point can be as readily calculated from the psychrometer as can the tension of vapor and its relative amount, if desired.

The daily range of humidity is considered much greater in the Atlantic States than in Great Britain, or in other countries of western Europe. As a general rule, the dew-point is here many degrees below the temperature of the atmosphere, which is thus considerably removed from saturation. The following comparison of mean temperature, &c., observed and calculated for Haddonfield, N. J., for 1864 and 1865, with the means for seventeen years at Chiswick, near London, will exhibit these facts, though not in so striking a manner as observations made at more arid points in the interior of the country would present:

A table exhibiting the temperature, dew-point, rain-fall, and evaporation at Haddonfield, New Jersey, and Chiswick, England.
1864Mean temperature of the year [°F]Mean dewpoint of the yearDryness or difference between termperature and dewpointRelative humidity of % of saturationPossible evaporation in a gentle breezeRain and snowPossible evaporation and rain-fall compared
From 1 sq. ft. in grains per minuteFrom 1 acre in gallons per dayFrom 1 acre in tonsAmount evaporated in inchesAmt. deposited as rain & snow, in inchesAmt. deposited as rain & snow, in tonsExcess of rainfall over evaporation, in inchesExcess of rainfall over evaporation, in tonsExcess of evaporation over rainfall, in inchesExcess of evaporation over rainfall, in tons
Haddonfield, New Jersey
Entire year52.7343.729.0172.222.272,4403,71232.88 43.79495410.911242
Summer73.0061.5011.5068.975.065,4842,10218.628.0390810.591294
Winter30.6724.006.6777.030.849031421.2613.171,48911.911,347
1865
Entire year53.1046.406.7020.441.801,9952,91326.3355.136,23628.803393
Summer73.6266.756.8781.613.323,5711,38212.3112.591,4230.3841
Winter34.5828.805.7885.240.828661401.2411.241,26810.001,128
Chiswick, near London, England
Mean of seventeen years49.8844.315.5783.701.321,4192,16119.1124.402,7605.29599
Summer62.2154.567.6577.602.682,9041,1159.86?5.00?565?4.86?550
Winter38.9535.643.3191.300.606452492.20?5.11?5782.91329

By means of the average temperature, the mean dew-point, and tables showing the evaporative force per minute in grains from a definite space, we may determine the amount of evaporation which may take place from a lake or the soil, in a calm, in a gentle breeze, or when a fresh breeze is blowing. The latter tables, prepared by Dr. Dalton, have been accepted as correct; and from them we have calculated the amount of evaporation as expressed in the accompanying table. A few remarks in explanation may be needed.

The mean temperature at Haddonfield, New Jersey, six miles southeast of Philadelphia, in 1864, being 52°.73, and the dew-point, by calculation, 43°.72, the difference indicating the dryness is found to be 9°.01, or nearly 50 per cent. greater than that for 1865, and 60 per cent. greater than that for seventeen years at Chiswick, near London. The summer of 1864 was remarkably dry, and the dryness expressed by the difference between the mean temperature and the dewpoint is as well pronounced, being 114°, or 75 per cent. greater than that of 1865, and 50 per cent. greater than the Chiswick mean for seventeen years. The relative-humidity expresses the same results. The winters of 1864 and 1865 did not differ widely, but were twice as dry as those of Chiswick. As respects evaporation, it would, of course, be expected to prove much more active in so dry an atmosphere than at places or in seasons more humid. Accordingly the possible vaporization at Haddonfield, New Jersey, for the entire year having been at the rate of about 2.27 grains of water per minute for one square foot, the average motion of the air being nearly equivalent to a gentle breeze, on which this rate of drying has been shown to attend, the corresponding values in other quantities, as gallons per day, or tons per year, and inches in depth, may be readily determined, or may be found in the foregoing table. Thus, in 1864, nearly 33 inches or 3,712 tons of water might have been evaporated from one square acre, the air moving in a gentle breeze. Had the air been at rest or calm, nearly 1,000 gallons less per day, and 1,400 tons less per annum, to each acre, might be evaporated, than if a fresh breeze prevailed for the same period. During a strong wind, or a high wind, this increase of evaporating power becomes much enlarged; and when very dry, as winds are at times in the Mississippi valley, it blasts vegetation as with a breath of flame.

In the dry summer of 1864 the evaporation was probably much greater than the rain-fall, as the soil was parched to powder, and vegetation depleted of its moisture, drawn from beneath the surface, apparently to the amount of nearly 10.59 inches, or about 1,300 tons for the season. In the summer of 1865, which in this district was not uniformly dry, the possible evaporation and rain-fall were about the same. In the summer of 1864 the possible evaporation at Haddonfield was nearly twice as great as for the average of summers at Chiswick. The excess of evaporation over rain-fall at the latter place is doubtful, our data being unreliable. The results arranged in the foregoing table must be accepted as approximations only, since accuracy cannot be attained where the elements are so difficult of authentication.1 Their general accordance with known facts renders them more reliable, while they serve to show the immense importance of the evaporating action which is constantly going on around us on so grand a scale.

The increased facilities for drying the soil existing in an open, cleared, level, cultivated country, become apparent on comparing the amount of water evaporated with the rain-fall at Haddonfield in 1864 and 1865, and with similar results, determined as correct, from actual measurements made near the headwaters of Anthony’s creek, a tributary of Green Brier creek, an affluent of the Kanawha river. The discharge of this creek, of which the area of drainage was carefully surveyed, was ascertained, by daily measurements: for one year, to amount to 70 per cent, of the rain-fall, and 65½ per cent. of the average fall for five consecutive years.2 The waters thus hastened off by the sloping mountain sides, or sunken among the leaves or into the soil or rocky crevices, and sheltered from evaporation by forests, restore a much’ larger proportion of the rain to the rivers directly. In this section, as generally in an open champaign country, where drying winds prevail and much land is exposed by tillage, evaporation may take place to the extent. of three-fourths of the rain-fall throughout the year, or more than. twice that fall for an entire summer. Hence the value of forests, as arresters of evaporation, or as barriers against the sweep of drying winds, becomes obvious.

If our reductions as tabulated appear excessive, we may refer to other results corroborative. Thus, at Ogdensburg, New York, in one year, 19.94 inches were evaporated during the summer months, and for the entire year 49.37 inches. At Syracuse, New York, in one year, 23.53 inches were evaporated in the summer, and 50.20 inches during the entire year. At Salem, Massachusetts, the result, of extensive observations, the annual evaporation was stated to amount to 56 inches; and the same was reported to have been the result at Cambridge, Massachusetts... Colonel Abert assumed, from many calculations, that the average evaporation for the summer, at Baltimore, Maryland, is 1991 inches, and that there escapes into the air from an open reservoir, in summer, twice as much water in the form of vapor as falls therein as rain. (Blodgett’s Climatology of the United States.) Dalton and Hoyle’s experiments on the actual amounts received and retained by the soil and sinking therein determined the annual evaporation in the moist climate of Manchester, England, to be 25 inches. A comparison. of our results with the above will enable the reader to decide upon their probable correctness. As respects the contrasted climates of America and Britain, the differences in dryness noted in the table are not dependent on the relative amounts of rain, for nearly twice as much falls at Haddonfield as at London in the course of a year. ‘he rain-fall at the latter place is, however, frequent and moderate; while at the former (and generally in the United States) the rains are heavy and of shorter continuance, alternated with longer seasons of fair, dry weather. The chief cause of the difference in dryness may be found in the fact that the humidity of Britain is borne over it from the vapor-laden ocean, while the prevailing westerly winds waft our land moisture away from us towards the sea, drying us, instead of increasing our store of vapor.

ON ATMOSPHERIC DRYNESS AS AN AID TO RADIATION AND PREVENTIVE OF UNSEASONABLE FROSTS

One of the peculiarities of the district of lower New Jersey, where frequent instrumental observations have been made by the writer, is a general freedom from excessive humidity, even during periods of very high heats. At no time during the months of June, July, or August, 1864, did the humidity of the air reach saturation; nor did it hold as much moisture as it was capable of absorbing. The climate is consequently, in a great measure, free from those seasons of extremely hot and oppressive weather so overpowering to many persons in some other localities. The summers are not, however, free from high heats; they are, on the contrary, very warm in districts remote from the sea—a maximum of 96° having been occasionally experienced. These, and many other seasons of extreme warmth, were not attended by excessive humidity, but by great dryness or low relative-humidity. Instead of approaching saturation, the amount of vapor in the air was generally but from forty to sixty per cent. of what it might have held at the high temperatures noted.

The long continuance of this low humidity is unfavorable to the growth of vegetation, and when reduced to a very low percentage, is the indirect cause or accompaniment of a fall in temperature in some instances fatal to young plants. If in June or July a few days of north or northwest wind, cool, dry, and absorbing moisture readily, blow over us, it bears away the moisture from the air and from the soil and plants beneath. _ On such days may be seen those beautiful white, massive, cumulus clouds which are produced by the elevation and subsequent rarefaction and cooling of large masses of air containing vapor. These clouds, which float so gracefully towards the east or southeast, “are but the visible capitals of invisible columns of humid air,” which are thus borne away from us. The consequences of this removal of vapor are soon felt, and that in a manner unmistakable, though until quite recently not clearly explained.

The new researches into the phenomena of heat, which have overturned the old hypothesis of caloric and substituted the theory of vibrations, have brought to light the extraordinary fact that vapor of water is opaque to the rays of heat of low intensity, such as that which proceeds from the soil and from plants by night; in other words, that the heat of the earth cannot be radiated or projected towards the sky if there exist in the air above the spot observed a large proportion of aqueous vapor. Through pure air, free from moisture, the heat may pass off as readily as if no air existed above the cooling region. It is believed that air saturated with moisture at the ordinary temperature absorbs more than five hundredths of the heat radiated from a metallic vessel filled with boiling water, and Professor Tyndall calculates that of the heat radiated from the earth’s surface warmed by the sun’s rays, one-tenth is intercepted by the aqueous vapor within ten feet of its surface, Hence the powerful influence of moist air upon the climate of the globe. Like a covering of glass, it allows the sun’s rays to reach the earth, but prevents, to a great extent, the loss by radiation of the heat thus communicated.

In accordance with this theory, it should be shown that the withdrawal of the sun from any region over which the atmosphere is dry, would be followed by quick refrigeration. It is said that the winters of Thibet are rendered almost unendurable from an uninterrupted outward radiation, unimpeded by aqueous vapor, and that everywhere the absence of the sun favors powerful radiation when the air is dry. “The removal for a single summer night of the aqueous vapor from the atmosphere that covers England would,” says Professor Tyndall, “be attended by the destruction of every plant which a freezing temperature would kill.” In the Sahara, where “the soil is fire and the wind is flame,” the refrigeration at night is painful to bear, so that ice is sometimes formed there. “In short,” says the Professor, “it may be safely predicted that wherever the air is dry the daily thermoimetric range, or the difference between the extremes of heat and cold, will be very great.” Illustrations of the truth of this position may not be out of place here. They may now be found wherever we turn, though until the genius of a Tyndall demonstrated the cause of the phenomena, we failed to perceive their connexion. The student should avail himself of the instructive and delightful pages of “Heat Considered as a Mode of Motion, by John Tyndall, F. R. S,” which is pronounced “ one of the most valuable and profound books which this generation has produced, eloquent, simple, and clear, exemplifying the double genius of discovery and exposition.” The title of this work indicates the theory of heat held by its author, the only one now held by scientific men—it is a mode of motion.

All great discoveries have been partially anticipated by keen observers, who could not wholly explain certain anomalous appearances, but whose shrewdness led them beyond the borders of the unknown. These results of Professor Tyndall were thus foretold by R. Russell, esq., of Scotland, who visited America in 1854 to study the effects of our climate upon agriculture, and whose lectures on meteorology may be found in the Smithsonian report for 1854. He asserts, on page 195 of that report, that “the influences of moisture in tempering the sun’s rays is a remarkable fact and well worthy of further investigation. When the dew-point is high, or the air is filled with moisture, radiation from the earth is prevented and the temperature of the night remains almost as high as that of the day. When the dew-point is low, the sun’s rays pass without absorption to the earth, and impart little of their heat directly to the air. The medium dew-points are therefore most favorable to extreme heat in the atmosphere, and the greater heat beyond the tropics is probably owing to this cause. The fact that the amount of moisture in the air regulates the temperature of the nights has _not received the attention it deserves.” The great amount of moisture in the air within the tropies is the cause of the warm and brilliant nights. Radiation from the airand ground, under these conditions, seems to lose its power. On the other hand, travellers in all parts of the world inform us, incidentally, as to the connexion between dry air and cold nights. Mr. Inglis, in his travels through Spain, relates that he was oppressed by the hot rays of the sun in the valley of Grenada while the hoar frost. was lying white in the shade. Eastgrn travellers in the desert often complain of the broiling heat of the air during the day, and of its chill temperature at night. Beautiful allusions to the same law are also found in scripture, where it is related that one of the greatest hardships which Jacob experienced while tending the flocks of Laban, was that through the “drought by day and the frosts by night, sleep departed from his eyes.” These conclusions are confirmed by recent travellers in a remarkable manner.  We need no longer doubt the stories of Captains Riley and Paddock, as told in their once incredible narratives, when they relate that the intense heat of the sun had scorched-and blistered their, bodies and limbs, so that they were covered with sores, . * * * — while as soon as the burning sun had sunk be- neath the horizon, the fresh wind cooled the earth, which became even cold before dark, * * * to be followed by fierce and chilling blasts of wind.

The experiments of Captain Sabine, made on the coast of Africa, show that while the sea breeze was blowing upon his station, the hygrometer denoted the dew-point to be about 60°; but when the wind blew strong from the land it sunk to 3749, the temperature of the air being 66°. Notwithstanding the heat of the evaporating surface of the Sahara, the burning sands of the desert yield so little vapor that there does not exist in the winds wafted to the coast, and which con- stitute the true harmattan, a greater force of vapor than that which rests upon the Polar seas; for at both places the constituent temperature of the vapor, or the point of deposition, is below 32°. The sea breeze above referred to contained eighty per cent. of relative-humidity, the land breeze from the Sahara less than twenty per cent. of the same, (Daniels’s Meteorological Essays, page 123.)

The desert and mountainous regions of our own continent furnish ample illustrations of these phenomena of radiation. Captain Beckwith, in his narrative of the Central Pacific Railroad survey, remarks : “We observed the greatest contrasts between the heat of the day and of the night in these mountain valleys, from noon to 3 p.m. the thermometer standing at 87° to 90°, and at night falling below the freezing point.”

Colonel Emory says: “On the 23d of October we retired with the thermometer at 70°, and awakened in the morning shivering, with the mercury marking 25°, notwithstanding our blankets were as dry as if we had slept in a house.” (Emory’s Military Reconnoissances in California, page 63.)

These low morning temperatures were found to characterize the whole country between Upper Mexico and the settlements near Great Salt Lake, the sunrise observations for three successive days being at 14° and 15°. At Salt Lake, Utah Territory, it is difficult to grow Indian corn, because of the extreme aridity of the air, though the mean temperature is 10° above that necessary in a moist climate. The local cooling at night, and the higher heats by day, are both unfavorable in this arid atmosphere.

R. E. Alison, who ascended the peak of Teneriffe in 1865, reports that “at the crater the extreme dryness of the atmosphere and the direct action of the sun’s rays were distressing. The lips cracked, the nails became brittle, and evaporation from the wet-bulb thermometer so rapid that it was necessary to watch it closely lest it should dry before an observation could be made. At the height of 8,000 feet he suffered more from radiation than from cold. In September the temperature in the shade was 40° Fahrenheit; the black bulb thermometer exposed to sunshine rose to 196°, or close to the boiling point of water, at that elevation. At times it reached 210° Fahrenheit at lower points, while-the nights were extremely cold, the dryness excessive, and the dew-point bee an as low as 40° to 50° Fahrenheit.” (Journal of Science, January, 1866.

To return to the researches of Professor Tyndall upon the cause of this intense radiation on mountain tops and on desert plains, we may, in a few words, state that a long series of experiments with instruments of delicate construction have demonstrated the truth of the hypothesis that these extreme reductions of temperature are due to absence of humidity. They also show that the presence of a large proportion of vapor, even less than saturation, acts as would a dam to flowing water, restraining the escape of heat by greedily absorbing it, and that though the air itself is a perfect vacuum as regards the rays of heat, the presence of humidity in considerable quantity renders it almost completely opaque to heat of radiation.

Such are the conclusions arrived at by the physicist in his laboratory. If true, they are of immense importance in their applications to meteorology, to climate, and to human comfort. Perhaps they will explain some anomalies in our experience, clear up some difficulties in the study of climate, and enable us to protect ourselves from some of the injurious effects which follow extreme dryness at certain critical periods. That they are great truths we have never seen demonstrated outside of the lecture-room; but if sound, they must find ample evidence to sustain them whenever instrumental observations shall have been properly applied thereto.

During the years 1864 and 1865, regular observations were made by the writer upon the temperature and humidity of his district, in Camden county, New Jersey. Extremes of atmospheric dryness were noted on several occasions during June and July of 1864, and at times in 1865. These extremes of low temperature appear to have been, in some way, dependent upon the periods of dryness— a connexion which was not suspected until after the perusal of the volume before named, in which is set forth, in a most luminous manner, the results reached by the distinguished physicist already adverted to.

On June 11th, 12th, and 13th, before dawn, there occurred the remarkable reduction of temperature to 43°, 44°, and 44° respectively—temperatures much lower, with one exception, than had been observed for nearly a month previous, and 21° to 22° lower than the mean for June observations at 7 a.m. This remarkable reduction of temperature was felt throughout all the northern States, from the extreme eastern point of Maine to Wisconsin, and from New Jersey to Missouri, and even in Utah. The coldest days in June at all these places were the 10th, 11th, 12th, 13th, and 14th; on the first day in the northern, on the 11th and 12th in the middle, and the 13th and 14th in the more southern and southwestern regions. Frost occurred over a wide region on the 10th to the 12th, from Maine to Minnesota, as far south as northern New Jersey, Pennsylvania, Ohio, Indiana, and Illinois. At Haddonfield no frost appeared, though the temperature was reduced almost to the verge of freezing, as indicated by a sheltered register minimum thermometer.

It may be said, in explanation of this extreme reduction of temperature over so wide a region, that it arose from sudden and grand displacement of the upper strata of cold dry air, by the upheaval of vast masses of the lower strata, buoyant with the vapor derived from the surface; or, in other words, from the derangement and subsequent descent of the cold upper current, the result of extensive thunder-storms. This theory is worthy of consideration. These changes possibly may have much modified the condition of dryness, and thus partially explain the advent of extreme cold.

Again, in July, 1864, we observed a remarkably low temperature before dawn of the 22d, when the self-registering thermometer stood at 50°; and again, on the 23d, at 469, at six feet above the soil—a narrow escape from frost. The same low temperatures were observed from Maine over all the northern States to Kansas, and southward to New Jersey and Pennsylvania. The reports do not correctly express the minimum temperatures by a self-register, and the reduction must have been several degrees lower than reported. On the morning of the 22d of July there was a slight frost at Baldwinsville, Massachusetts; also at Columbia, Connecticut, and Tioga, Pennsylvania.

Now, some cause acting over a wide region must be sought for to account for the widespread reduction of temperature on the days noted. Will the diminution of the due proportion of humidity in the air over this region adequately explain it? Will the westwardly winds, with their drying and absorbing action, prove to be the agents by which radiation is permitted more vigorously to proceed, and thereby effect the changes which come over us?

Let us turn to our meteorological notes and observe the figures there recorded.  At Haddonfield the low temperatures were observed on the 11th, 12th, and 13th of June, 1864. On the mornings of the same days the tension of vapor was but .262 to .822, which were lower measures than were observed on any other mornings during the month, except on the 7th, when it sunk to 50°. On the evening of the 6th the humidity had been abundant, more than twice as abundant as on the evenings previous to the days above named. The tension of vapor noted on the mornings of the 11th, 12th, and 13th was less than three- quarters of the average for the month at 7 a. m., and but one-third of that prevailing on several occasions. On the 28th and 29th of June the self-register thermometer indicated, before dawn, 50° and 51° respectively, and the amount of vapor exhibited a corresponding low degree of tension, being but .389 and .356 respectively. No very low degrees of humidity were noted in July until on the mornings of the 22d and 23d, when it fell to .296 and .865, which were remarkable, and’ were accompanied by the low temperatures of 50° and 46° respectively. The amount of vapor in the air was noticed to be but about half the mean generally present, and one-third of that often observed. At 2: p- m. of the 22d but 22.8 per cent., and on the 23d but 26.6 per cent. of relative- humidity were noted, numbers indicative of extreme dryness—the first expressing the fact that but little more than one-fifth and the last about one- fourth of the vapor capable of being sustained in the air at the temperature then prevailing was actually present.

Now, on the 9th of June, at 9 p. m., a northwest wind had begun to raise a gentle breeze; a north wind continued all day; but it was nearly calm in the evening of the 10th. A northwest wind was blowing on the morning of the 11th, from southeast, for a short time, at noon of that day, but again north all day of the 12th and part of the 13th. All day of the 9th, 10th, 11th, and 12th, the masses of cirrus and cirro-cumulus in those heavy white separated clouds sailing overhead or piled in the horizon, were moving first from the south and southwest, then from north and northwest, having been carried up beyond the influence of the surface currents or counter trades into those which were pouring: over and descending, to become in turn the northwest dry wind of the surface. These cumulus clouds, which are produced by the elevation and subsequent rarefaction of large masses of air containing vapor, were doubtless “the visible capitals of those invisible columns of humid air” which the absorbing northwest wind was drawing from the surface of the earth. All the circumstances favorable to the rapid drying of the air near the earth were at work, and the humidity was consequently greatly reduced. The results promised by reduction in the amount of vapor present followed, and we experienced excessive cold, in accordance with the theory of Professor Tyndall. The blanket of vapor had been removed, and the heat escaped into space.

On the 22d and 23d of July the same general conditions of drying winds, accompanied by extreme atmospheric dryness, were present. On the 22d, the afternoon of the day before the reduction of the temperature to 46°, a neighboring farmer remarked the extreme aridity of his oats, saying they “dried before they reached the ground” while cutting them. During the 22d, 23d, and 24th, the days of lowest temperature by the self-register thermometer, a smoky haze was observed, extending from Maine over New Hampshire, Vermont, Massachusetts, New York, New Jersey, Pennsylvania, Ohio, Michigan, and further west. An extended drought prevailed, the earth being as dry as the air above it, and north and northwest winds of very gentle action passed over us by day while the nights were calm. This calmness by night was also noticed early in June, when the lowest temperatures were observed, and was highly favorable to radiation. On the 22d of July, at 2 p. m., the force of vapor or pressure in inches on the barometer was but .188, which is lower than we have ever observed it during summer and autumn, and lower than is sometimes noticed even at the freezing point. No abnormal reduction of temperature or of humidity appeared in August of 1864.

Here, again, it might be surmised that the reduction of temperature was due solely to the descent of the colder air of the upper atmosphere, drawn from sub- arctic regions, were the periods of extreme cold always accompanied by northerly winds; but such is not the case at all times, though how far such north winds may have affected the temperature of our surface currents from other quarters, we cannot determine. The presence of an extreme drought extending over many hundred miles, and the canopy of haze undisturbed for several weeks, spread over all the northern States, seem to preclude the probability of the existence at the time of such descending currents from the north as would be adequate to the production of such wide-spread cold. A few local storms or mountain squalls may have been noted, but these did not disturb the haze, and the severity of the drought indicates that no rain-storms occurred. It seems much more probable that the west and northwest surface winds, whether from the Rocky mountains or the western deserts, were drying the surface,3 and thus indirectly cooling us, rather than that they were the direct cause of the cold. Moreover, had this cooling been due directly to the descent of the cold upper currents, the temperature at midday would have been much reduced, which was not generally the case; some of the mornings of extreme cold having been preceded and followed by high heat at midday, just as would result from the passage of the sun’s rays more freely through an atmosphere deficient in aqueous vapor. It will also be remembered that, in general, reduction of temperature, while it diminishes the capacity for humidity, tends to render that actually existing in the air proportionally greater, or to increase the relative-humidity. In the cases we consider, the relative-humidity and the temperature decline simultaneously, or, to speak with precision, the former appears to: precede the latter as does a cause precede or keep pace with an effect. Whatever may be the cause, direct or indirect, of our midsummer cold, it is worthy the investigation of meteorologists, and should commend itself to American observers especially.

The experience of the writer in 1865, is confirmatory of the asserted connexion between dryness and extreme low temperatures. In June, 1865, the minima temperatures were not quite as extreme as in June, 1864. Very heavy rains fell on several occasions, and the atmosphere was remarkably loaded with vapor, often to the amount of .780 to .890, at one time to .914 and .942 inch of tension, as measured by the barometer. The average force of vapor for the month was .667, while that for June, 1864, was but .492; the lowest force of vapor for June, 1865, was .421, or about that of the mean for the entire month of the previous year, thus presenting a marked contrast. There were in June a few cool mornings, as that of the 12th, when, after a day of low-absolute relative-humidity, the minimum before day was 53°, and the dew heavy, showing a much lower reduction under the open sky. Most of the grape-vines had bloomed, the Herbemont being then in blossom. On June 19th mildew was observed on the Isabella, Catawba, and Herbemont—the consequence of dryness and reduction of temperature.

On the 20th of June, 1865, a heavy rain fell and the air continued loaded with moisture, .816 of an inch having been observed on that day, and on the 24th, .784 inch of tension. On the 23d, the relative-humidity was remarkably low and the tension reduced to one-half of the above numbers, and the register- thermometer indicated 62½° on the morning of the 24th, and a fog was brought over from the southeast, This high humidity and sudden reduction of moisture and of temperature (for the true minimum was perhaps 10° to 14° lower) had its usual effect; for on the 25th of June the young Catawba grapes were rotting. The high temperature of the soil which, at one foot deep, stood at 76° and 77° until 9 p. m., and parted with but three or four degrees all night, may have contributed to this result.

In July, 1865, high heats and moisture alternated with reduction of vapor, and with it low night temperatures, and the grapes were again rotting. The humidity was most excessive in the earlier part of the month, when the rotting was most observed. This at one time reached the high measure of .973 inch of tension, or nearly twelve grains of vapor in the cubic foot, with a maximum temperature of 94° on the 7th. The force or tension of vapor, or absolute humidity, as it might be termed, varied from .371 to .973 inch during the month of July, the first or lowest tension having been observed on the evening preceding the morning on which the lowest temperature of 53° was noted. Though but 1.95 inch of rain fell, the relative-humidity was nearly forty per cent. greater than in July, 1864, when 3.12 inches were deposited. On the evenings of the 13th, 14th, and 15th, the low relative-humidity appeared, and the lowest temperatures of the month were observed, the register-thermometer having indicated 53½° on the morning of the 14th, and 53° on the 15th and 16th, which were very unfavorable extremes. These variations from the temperature at or after 2 p. m. to that of the next morning: before dawn, were thus in several instances upwards of 26° to 30°, as expressed by the shaded and sheltered thermometers; but under the open sky, exposed to the burning sun by day, as on the 14th, and the radiation on a clear night through an excessively dry atmosphere which was present, vegetation probably endured a range of nearly or quite 100° of Fahrenheit, highly injurious as the consequences proved, for the grape crop was entirely destroyed in this section of New Jersey, as well as generally around Philadelphia.

The first half of September, 1865; appeared to be very unpropitious for the grape but our previous experience had been conclusive, mildew and rot having one their worst with the native vines, and the foreign, under glass, alone remained on which their destructive agency could work. From the 1st to the 15th, the absolute and relative humidity were excessive, and the 14th was among the most oppressive ever remembered or recorded by the writer, frequently rising to saturation.. Though the heat was not in excess, the abundant moisture rendered some of the above days painful to endure, the feeling being, at times, that accompanying immersion in a steam bath. Our Black Hamburg grapes which had not already ripened under glass, were dissolved in a mass of rottenness in consequence of suffocation in this vapor-laden atmosphere.

No extreme low temperature appeared before dawn until the 16th and 17th, when, with the first appearance of reduced humidity, came also low minimum, though during the prevalence of the moisture the nights had been equally clear.4

The foregoing facts and comparisons appear to furnish strong evidence of the close connexion between diminution of humidity and reduction of temperature, and to confirm the assertion of Prof. Tyndall, that their relation is that of cause and effect—that loss of humidity continued through several days, from the action of a drying wind during a dry season, prepares for the escape of the heat of the earth by night, through unimpeded radiation, into space.

If a cause for the reduction of temperature has been found in diminution of humidity in the air, over any region, a remedy must be sought in protection from influences causing excessive dryness. A remedy applicable to the wide northern territory, where these low temperatures sometimes occur during the critical periods of early spring, the direct result of the precipitate descent of cold air from the high region of the atmosphere, we fear, will not be found; but that in the lower regions, where the extremes are not so great and where they merely border on the freezing temperature, perhaps they may be applied with considerable promise of success.

Now, let us ask ourselves what are the causes operating around or above us, producing excessive dryness in our atmosphere and in the soil? A west or northwest wind is undoubtedly a cause, largely, if not wholly, competent, to reduce the amount of vapor in the air, and to render it incapable of preventing the escape of heat absolved by the earth during the day. We know that the winds which are flowing towards the northeast from the regions of the tropics, part with their moisture in rains and showers over the temperate districts. We know that on the Pacific coast the prevalence of westerly winds gives a great uniformity to the temperature, and that most of the rains come from that quarter; that the cloud-bearing winds, by passing up the slopes of the Rocky mountains, lose their moisture by condensation into clouds and deposition as rain and snow, so that as they pass eastward they are dry winds, and must so continue over the vast desert region, arid and waste, which extends from the mountains on the west to the borders of the Mississippi valley on the east. These conclusions seem so well established, that it has been well remarked of the northern Atlantic States, says Robert Russell, “So long as the westerly winds continue to blow in winter, there is no cessation of your cold; and so long as they continue to blow in a broad, regular stream in summer, there is no end to your drought.” (Smithsonian Report, 1854.)

A great drying agent may then be generally found in the westerly wind,3 sometimes in that from the northwest. The only protection from their baleful influences appears to be ample and systematic planting of dense evergreen trees upon the west and northwest sides of orchards, vineyards, and gardens generally. The northeast also should be sheltered. We have been reckless in using the gift of Providence to our fathers... We have razed with ruthless hand the forests which were both the ornament of our region and the safeguard from the ravages of cold. The truest wisdom may be learned in the school of nature, and it is only as man imitates the plans of the Creator that he can hope to prosper.

As mitigators of the severity of radiation, the introduction of shelter trellises is highly promising. But in more northern districts, where this method may not be available, it were better to abandon all attempts to cultivate our tender fruits, except in regions where the severity of dryness and of cold in midsummer is-ameliorated by the presence of widely protecting waters. It is only in these sheltered regions that we can now hope to find a climate fitted to the regular production of our leading varieties of fruits, and it is here only that we shall be able to meet with success in grape culture through a lengthened series of years.   As respects the value of forest screens, a large body of testimony might be advanced; a few illustrations will suffice.

ON THE VALUE OF SCATTERING BELTS OF FOREST TREES AS PROTECTORS FROM DRYING WINDS AND EQUALIZERS OF TEMPERATURE.

The decline of many varieties of fruits once successfully grown and highly esteemed, has often been ascribed to the exhaustion of the elements in the soil necessary to healthy growth and fruiting; but we apprehend that this deterioration is much more largely due to the distribution of our forests—to the removal of those protecting screens which once sheltered, not only from extremes of cold, but also from extremes of dryness.

It is a common experience that our best varieties of fruit trees are more liable to disease, and that their fruit is generally inferior in quantity and quality to that known to our fathers. Negligent culture and increased age of the trees, it is true, may have had some influence; but even more skilful culture applied to young and thrifty trees is not attended by the success formerly common. Our apples are more frequently scabbed and distorted; our pears so knotty, cracked, and hard, that we need not seek Australian pears (which are said to be of wood) for distortions or perversions of this fruit.

Though the practice of gardeners in Europe may not be generally applicable in America, and those who expatriate themselves to settle among us soon part with many of their home-bred customs, it were well if one of the universal rules of English gardening still held sway among us. An English garden is seldom seen without a wall or hedge surrounding, it, and their fruit grounds are also generally protected in the same way. We have been under the impression that their walls are necessary in order to produce, by reflection, a higher heat for ripening the peach and the apricot, which they doubtless do cause to mature more perfectly; but any one who reads their best horticultural treatises will find that they are also intended as shelter from what are deemed blasting winds. Hear an old authority, the learned and pious John Lawrence, author of the once very popular “Gentleman’s Recreations,” a work now one hundred and fifty years old, but still sound and valuable: “One great cause of the want of fruit in many gardens is a lying too much open and exposed to the winds, especially the west and southwest winds; which, in many parts of the year, make terrible havoc and desolation in our island, not only by blasting the fruit in the spring, but by chilling and starving the fruit all the summer, so as to hinder it coming to any due maturity.” If such are the consequences of the west and southwest winds, which are comparatively mild in England, what would we reasonably expect should result from the free range over our orchards of our westerly and northerly winds, and the raw damp northeasters of our northern States? Can we continue to feel any doubt that in this free exposure to such winds, now more than ever before free to blow where they list, we are generally so unsuccessful in our attempts to grow good and fair fruit in the open country?

As if to offer the fullest confirmation to the truth of the assumption that shelter is the sine qua non in fruit culture, we have the experience of our city friends, who, in horticultural efforts, always surpass us in the country, whether we regard quantity, quality, or beauty of the product. Any one familiar with the exhibitions of the Pennsylvania Horticultural Society knows that Herbemont and Catawbas grown in the city of Philadelphia surpass those grown in the country.  Every one knows that a venerable amateur, Isaac Baxter, on a city lot surrounded by brick and mortar, has, for a long series of years, grown such butter pears as no resident of the country around has. been able to exhibit, Let any one visit the rooms of the Mercantile Library in Philadelphia, and look upon a fine old butter pear tree standing in the back yard of the Dispensary, sheltered by walls on the northwest, north, and northeast, and note in the season the fruitage—smooth, golden, and tempting—and believe, if he can, that such pears cannot still be grown as of old under favorable circumstances, sheltered from drying winds and cold. The vine and the pear, especially, require a climate moist and warm; and shelter from drying and cooling winds, with proper southern exposure, are the prerequisites for supplying these conditions. It is to the protection from the northwest and northeast winds, with perhaps some elevation of temperature due to reflection, and the generally increased warmth of the city, that we must ascribe the success of our city amateur pomologists.

An amateur gardener in the city of Camden, New Jersey, whose grounds are surrounded by a board fence, and who is, at the same time, affected by the protecting influences flung around it by the damp atmosphere of the Delaware, (but one hundred yards distant,) produced pears upon his dwarf trees greatly exceeding any raised by his neighbors further removed from the river shore. Smooth and waxen fruits grow upon his trees, while theirs are knotty, gnarled, and worthless, because exposed to the pelting northeast, or the biting and drying northwest, with its keen and eager airs.

The distinguished meteorologist, Frederick Daniels, by whom the first regular and accurate observations on the dryness and moisture of the air were made, asserts that excessive exhalation is very injurious to many of the processes of vegetation, and that no small proportion of what is commonly called blight may be attributed to this alone—that evaporation is increased in a prodigiously rapid ratio with the velocity of the wind, and that anything which retards its motion is very efficacious in diminishing these exhalations from the leaves of plants. He moreover adds, that in seasons of extreme dryness tender fruits are much more liable to injury, and that artificial shelters by means of walls, palings, hedges, or evergreen screens that will break the force of the blasts, are the most efficacious methods of preventing the evils of excessive drying.

To the foregoing illustrations of the great value of the kind of protection suggested may be appended evidence of the great injury resulting from the removal of the shelters originally planted in our forest land. A few of this character may suffice, but a heavy mass of evidence could be adduced, all expressing the same great truth. Man is rashly destroying the great regulators of the climate, while in his ignorance or indifference he is making no compensation therefor, by the assiduous replanting of trees.

In the Ohio Pomological Society’s report for 1864 appeared the following pertinent remarks by Dr. Peticolas, a devoted pomologist, of Mount Carmel, Ohio, now deceased. He stated that “out of one hundred and twenty or one hundred and thirty varieties of apple trees in bearing, it is difficult to select six kinds of good merchantable winter apples, because the product is not perfect, though it may be abundant. his imperfection is caused by the never-failing mildew or scab to which our apples are subject. Although some seasons are not quite as bad as others, still one-half or more, as a general rule, are unfit for market, and it is really humiliating to think that we who, a few years ago, boasted of the superiority of our fruit as compared with that of our eastern friends, (of western New York,) should now be obliged to acknowledge that they surpass us. Now, why is this? Why should such a change have taken place? No such alteration, that I am aware of, has taken place in the east; their apples are as fair and as good now as they were twenty or thirty years ago. Some of our varieties are less prolific than they were fifteen years ago. Rambos then bore, at seven years old, ten bushels of good fruit, but since have never borne over four our five, even in the most favorable. seasons, and these but inferior fruit. Redstreaks, the same time and age, bore thirteen bushels, but have never in any season since borne more than three or four of comparatively poor fruit. Nor can this change be attributed to the age of the tree, for trees of nearly all ages, of the same varieties, were nearly as unproductive. The White Bellefleur was formerly one of the finest and best apples, but can no longer be realized as the same, being now so knotty and scabby, and producing but one- fourth of its former yield. The White Pearmain was another of the best keeping and finest dessert apples, but it no longer is even fit to look at, being perfectly disfigured with the scab. Most of the others were in the same condition.” Our pomologist, so desponding, does not consider it of much import, to point out the cause of this evil, because he is satisfied, from long observation, that it is entirely owing to variations in temperature, and believes it therefore entirely beyond our control. Herein we deem him somewhat mistaken. He asks the question, “Why should our climate have become so different from what it was formerly?”  and then cites his observations as follows: His vines when grown on an arbor suffered badly from rotting after bearing a few years, but where the vines had grown sufficiently, and had reached the side of the house to which they were tacked, the fruit was fine and as sound as possible. This result he ascribes to the heat absorbed by the house during the day, and given out by conduction or radiation at night, thereby equalizing the measure-of temperature.

Every one who has a vineyard, he further remarks, must have observed that the mildew and rot supervene after some sudden change in the temperature, particularly when accompanied by rain. Now, the same effect takes place with apples and other fruits. Prince’s Harvest was formerly one of our best and earliest apples for market, but the doctor had ten trees from which he had not picked ten perfect specimens in ten years, although they bore quite abundantly, the fruit being especially affected by mildew and cracked badly. This induced him to observe this variety very closely for the last five or six years, and he discovered that spots of mildew invariably formed on the young fruit immediately after a cold night, when the thermometer had indicated a change of 20 to 30 degrees.

This growth of mildew takes place when the apples are of various sizes, from the earliest formation to that of hickory nuts.  These fungus growths appear as dark-colored spots, which arrest the growth of the apple immediately beneath, causing it to become distorted, while the expansion and contraction bring on diseased action, which results in the cracking and general scabbiness of the fruit.

Dr. Peticolas well remarks that no change has taken place in the climate of western New York, where apples are as fair and as good as they were twenty or thirty years ago—failing to perceive that the injury to the apples of Ohio has arisen from the changes man has wrought upon the country by indiscriminate felling of the forests. He did not perceive that the climate of western New York was preserved uniform in its measures of atmospheric humidity, and protected in a great degree from those extremes of which he complains, and which are not only extremes of cold, but also extremes of dryness, quite as unfavorable.

While conducting an extensive correspondence during the past winter, for the purpose of gaining information respecting the character of the climate of Michigan, and learning the opinions and experience of both scientific and practical men, it was interesting to perceive the perfect accordance in which they wrote respecting the effects of the removal of the forests. Says Dr. Kedzie, of the Agricultural College, Lansing: "The meteorological changes wrought by the destruction of the forests in Michigan are well marked. Krom 1828 to 1841 the peach crop in Lenawee county was as reliable as any fruit crop. The trees needed no protection and received but little care, and usually bore an enormous crop, followed by two years of smaller product, thus being abundant every third year. Now, in 1866, this fruit is only raised in situations protected in some manner from southwest winds, and the experience for fourteen years has been the same as at present. In 1852, and prior thereto, peaches were grown in Eaton county, near the centre of Michigan, in abundance, however exposed; at present they are a rarity except in guarded places. Thirty years ago a frost that would injure the corn in the spring, or during the usual growing months, from May to October, was almost unknown; at present it is an element entering into the calculations of every prudent farmer, so frequently do such frosts occur. The aspects of the district above referred to have been changed by the woodman’s axe, and with the last forest-clearing the peach has failed, until at present no reliance can be placed upon it except near Lake Michigan.”

Says T. T. Lyon, of Plymouth, Michigan, one of the most experienced pomologists of the State: “The peach crop during the last fourteen years has failed four years out of five from winter-killing of the fruit buds, and, occasionally, of the trees, although previously it was reasonably certain.”

The above testimony is confirmed throughout the West, and we are happy to perceive that the pomologists of Illinois are agitating the subject of tree planting on their extensive natural prairies. To the citizens of that great State planting is a subject of vast significance. A writer in the: Prairie Farmer, whose enthusiastic spirit is worthy of all praise, exclaims: "Who can compute the amount of winter grain, of fruit,of tender shrubs, destroyed by the intensely cold sweeping blasts which rave over the prairies of Illinois? The question comes home to all the residents of such districts: Can nothing be done to soften the rigor of such sweeping storms? Yes; stud these prairies with belts and groves, with screens of evergreen and deciduous trees. Plant the railroads and highways with rapidly-growing trees, in double or treble rows, upon. the sides from which drifting snows accumulate, and carefully attend to them after planting. The money spent in clearing, and keeping clear, the tracks during a heavy storm, upon, one of the western railroads, would have purchased trees or cuttings sufficient to have planted the entire line of road, which, in four or five years, would have grown to a perfect barrier against accumulating snow-drifts.  The benefit arising from planting trees would not stop with the saving of money to the corporations, and with the saving of life and suffering to the people. The crops would be increased in certainty and amount, the health-giving fruits secured to us, domestic animals made comfortable and thrifty, and the surface of the country would become beautiful beyond conception. Do not forget the lesson the extreme storms of cold should teach us. Let tree-planting go on henceforth with renewed earnestness and care, and anon we may laugh at the elements, and point with pride to the wonderful transformation the human hand has accomplished.”3

It is the prevailing opinion that forest protection is more demanded during winter and early spring, but the experience of many pomologists points to its influence in early summer as quite as valuable. The destructive blighting which results from rapid drying by the absorbing currents of westerly winds during seasons of low, relative humidity, and consequent sudden increase of cold, has already been dwelt upon. The experience of Dr. Peticolas is confirmatory of the necessity for shelter during thd fruit-forming season, and is in harmony with that of pomologists in the East, and we are convinced that belts of trees in an open country are absolutely necessary for protection from summer extremes of dryness and of cold. In our own district our winters are generally mild, and we need but little shelter from northern winds; but after the apple has set its fruit it is generally cut off or mildewed by raw northeast storms in orchards open to their range; but. where protected therefrom a crop is much more assured.

Says General J. T. Worthington, of Chillicothe, Ohio, in the Ohio Pomological Society’s report, 1864: “I become every year more convinced of the necessity of belts of trees in our climate of extremes to protect the annual crops from the late frosts and the fervid suns of July, August, and September; and I verily believe that if one-third of the land were devoted to belts of fruit and other valuable trees, the remaining two-thirds would produce as much as the whole without such shelter, even in average years, and far more in extreme ones; but I fear it is too early to preach planting trees to a generation which considers it the chief end of man to destroy them.” There appears to be no room to doubt that greater dryness of the air is a result of the removal of the forests, and that the earth then ceases to be equally moist, or the springs to furnish an equal quantity of water. It is the experience of ages in various countries that the presence of forests really makes the climate comparatively wet, and their removal makes it dry. It is not conceivable that they do this by absorbing vapor from the atmosphere, converting it into water, conveying it to their roots, and thus furnishing a supply to the ground; for this would make the atmosphere drier, and it is known that it is made more moist by their presence. If forests do cause the climate to become more moist and springs to flow more abundantly, as is generally declared, it can only be by causing more rain to fall. The progressive diminution of rain in the south of Europe is ascribed to the destruction of the mountain woods; and the diminished supply of water to ponds in our immediate district is known to be closely connected with the removal of our trees. It is curious, however, to observe that, in the latter instance, extensive under-draining has, in a great measure, restored the supply driven from springs; undue evaporation having been thus checked by facilitating the descent and gradual withdrawal of water from below. The under- drainage was, of course, chiefly applied to lands formerly marshy, or holding water near the surface. When lands are very widely cleared, extensive under- draining may prove injurious. Already the want of calculation and of forethought on the part of many improvers of land has been shown by their ill-judged extension of drainage. The rain falls on the land, and in a few hours it is removed from the soil and carried off by the brooks and rivers to the sea; consequently when a season of dry weather supervenes, the farmer finds his crop perish for want of water. In England, where these results have appeared, irrigation has, all at once, become the question of the hour, and the subject is being pressed upon the consideration of agriculturists——Journal of Science, January, 1866.

The action of forests in adding to the rain-fall, appears to be due to their offering an obstruction to the free flow of currents loaded with vapor, and the upward tendener such obstructions give to the air, by which it is piled up and retarded until aveumulated at sufficiently high elevations to induce condensation into clouds and rain. This is one of the regular effects of mountain ridges, and-any cause which shall, in like manner, force the air to rise in any particular locality may produce a similar result. The friction against the surface of the level earth impedes the free motion of air or winds, and that which follows tends to pile up upon the back of that resting on the earth, and that behind to climb still higher. If, then, the impediment of a dense forest be added to the obstruction already existing to free motion, the ascent of the strata of air, will increase according to the force of the wind bearing vapor with it. When this storm encounters a forest, the resistance must be materially augmented, and the retardation of the strata becomes greater, the overlapping and ascent of the current increased, more abundant condensation takes place, and more rain falls, and the district thus becomes more wet than it would have been had the bare ground alone been left to retard the progress of the lower portions of the wind.  Forests, therefore, cause the surface currents to rise higher upon their sides, as up an inclined plane, and to attain a great height, thereby affecting a district as would mountains of moderate elevation.—Hopkins’s Meteorological Essays.

While we write, it is announced in the daily papers that the inhabitants of the Cape Verde islands are again in distress from famine through lack of rain. Having destroyed their forests they suffer terribly from periodical droughts. From 1830 to 1833 no rain is said to have fallen, and 30,000 people perished, or more than one-third of the population. Though it has been proposed to replant the forests, such is the ignorance and indolence of the people that little has been done towards restoration Philadelphia Inquirer, May 17, 1866.

Many well attested instances of local change of climate might be cited, most of which are to be referred to the influence of forests as a shelter against cold winds. To supply the extraordinary demand for Italian iron, occasioned by the exclusion of English iron in the time of Napoleon I, the furnaces of the valleys of Berganio were stimulated to great activity. The ordinary production of charcoal not sufficing to feed the furnaces and the forges, the woods were felled, the copses cut before their time, and the whole economy of the forest was deranged. At Piazzatorre there was such a devastation of the woods, and consequently such an increased severity of climate, that maize no longer ripened. An association, formed for the purpose, effected the. restoration of the forests, and maize flourishes again in the fields of Piazzatorre.”

Similar ameliorations have been produced by plantations in Belgium, and a district redeemed from sterility by simply planting regular rows of trees, the oldest of which is not forty years of age. While the tempest is violently agitating their tops, the air a little below is still, and sands the most barren have, under their protection, been transformed into fertile fields. For many illustrations of the value of forest shelters, as well as proofs of the destructive activity of man, see that very valuable and instructive work, “Man and Nature; or, Physical Geography as modified by Human Action,” by Geo. P. Marsh; published by Chas. Scribner, New York, 1864.

Our fathers were, perhaps, wise in their generation when they so vigorously protested against the right of the King to mark the best trees in the New World with his broad arrow, and reserve them for royal use; but it would have been well for them had they early enacted stringent laws against indiscriminate destruction of forests.

A terrible scourge, and often exercised, was the assumed right, the worst conquerors and tyrants of old usurped, of destroying the forests of the prostrate enemy. Even among the ancient Greeks, barbarous as was their code of war, (for all war is barbarous,) it was considered an unpardonable offence to cut down the olive trees in an enemy’s country, and the single word dendrotomein, the feller of trees, conveyed, in their apprehension, the idea of the most barbarous forms of devastation.5  Are we less wise, less regardful of our own interests and of those of our children—we, who boast ourselves “the most enlightened"— than were the semi-barbarous Greeks, of the interest of their enemies? Are we not devastating the fair face of our country, not, it is true, by destroying our fruit trees directly, but as surely, though indirectly, by our ravages among the forest shelters of our great inheritance, while we remorselessly consume the material for the fires, the machinery and dwellings of our children’s children? Is it not high time that we had a Commissioner of Woods and Forests, and enactments regulating felling and planting, and enclosing them? We act as if our forests were inexhaustible; let us take warning by the experience of Europeans, who once thought as we now do, but were obliged, too late, to enact laws to preserve their timber and save a wreck from further destruction. In some parts of Germany no farmer is permitted to fell a tree without showing that he has planted another; and it is an inviolate custom in some German districts that a man must produce a certificate that he has set a certain number of walnut trees before he is permitted to marry. Wise precautions against the day of calamity, which the entire removal of the trees would surely bring upon them.

We are blindly following our instincts as to what may conduce to our personal and present advantage, regardless of the wide-spread evils that will assuredly flow from changes brought about by our individual labors of destruction. Let us also bear in mind that we are but tenants of this earth, not owners in perpertuity, and have no moral right to injure the inheritance of those who succeed us; but it is our duty to leave this world better than we found it. Not to desire to do this, is unchristian—is barbarous. Plant, then, trees; teach your children to plant trees and to love them. Again, I say, plant trees, and if you can find no other time to plant trees, arise at midnight and plant them.

ON HORIZONTAL SHELTER AS A PROTECTION FROM THE VINE MILDEW.

Among the remedies which have been proposed, whereby we may avoid the injurious effects of excessive radiation on dry nights, there are two which appear worthy of trial on an extended scale, as they have proved of much value when applied to a limited extent.

Every person who has trained vines on his out-houses has noticed, in seasons when they have suffered from mildew, that the branches which were sheltered by a projecting coping or eave were almost invariably free from injury; and that the grapes were ripened under this shelter, while shrivelled or decayed on the rest of the vine. Such has been the result of our observations, both at home and abroad, and furnishes renewed evidence that mildew and blight are generally, if not always, induced by extreme radiation at night.

The first proposed remedy we will notice is not new or untried, but can be traced back nearly one hundred and fifty years. In that excellent practical work, “The Fruit Garden Kalender,” by John Lawrence, M. A., London, 1718, will be found the following: “The great misfortune which we, in this island, suffer with respect to our late fruit, is the unconstancy of the weather, and the great difference of ten times betwixt our nights and days,-as to heat and cold; for we do not seem so much to want hotter days as less cold at nights.” * * * Referring to “the perpendicular frosts and mists which fall so frequently in spring and autumn, and cause such fatal destruction,” he says: “But were it any way practicable, nothing could more effectually bring Italy into England than a contrivance to take off the influence of our cold nights and uncertain weather. This I am persuaded might, in good measure, be done with no great charge or trouble, by means of low ordinary espaliers (trellises,) about two feet high, along the several rows of vines, to which. their shoots might be carried horizontally and fastened, and the fruit itself likewise defended by horizontal shelter fixed on the top of the espaliers, made of coarse narrow planks, with a convex superfices to throw off the wet.” Again, in the “Gentleman’s Recreation,” by the same author, he remarks, “Now these hints proceeded, I think, upon a right supposition that most of our frosts and blasts, both in spring and summer, fall perpendicularly, * * * and therefore the more anything lies open and exposed to this perpendicular descent of vapors, the more will it be subject to be frozen, or, which is the same thing, blasted; the truth of which is confirmed to us both by reason and experience. This, therefore, being the true state of the case with respect to most of our destructive blasts, a little philosophy will teach us that horizontal shelters are the best guard and defence against perpendicular frosts.” The above was written nearly a century before the phenomena attending the formation of dew and frost were comprehended, and nearly a century and a half before the true theory of nocturnal radiation was announced by Professor Tyndall; yet the facts recorded and the reasoning employed harmonize completely with the doctrine of the latter philosopher.

Our ancient amateur gardener does not limit himself to horizontal shelters, as above described, extending along the top of a low trellis; but recommends a succession of short projecting tiles from a wall, or boards from a trellis, one above the other, a foot or more apart, with openings between them through which the arms and stronger branches of the vines may pass upwards; while under each of these short boards the shorter branches and fruit may be protected from the “perpendicular frosts,” or, as we would now express it, from direct radiation towards an unclouded sky, and through an atmosphere deprived of its heat-absorbing and sheltering vapor. The experience of the projector of this ingenious plan of protecting vines and wall fruit he records as “highly satisfactory, especially as respects peaches, figs and grapes, which in many cold summers, without such helps, would never be ripe at all;” and “that horizontal shelters do really accelerate the ripening of fruit has been confirmed by experience.”

As it is now understood that the state of the atmosphere is the predisposing cause of the check to vegetation, which prepares for the access of mildew, and that it is to deficient humidity both in the air around the vine and in the superficial stratum, whereby an excessive radiation of heat by night is encouraged, it would appear highly probable that the mode of protection suggested and applied by Mr. Lawrence one hundred and fifty years ago, in England, would be found adapted to our own needs. Nor has it been entirely overlooked. The experience of William Saunders, the excellent superintendent of the Propagating Garden at Washington, has recommended a protecting grape trellis, which has its prototype in the horizontal shelters of the English gardener. That these protectors have proven valuable, is shown by the testimony of E. W. Herendeen, of Macedon, New York, who visited the “experimental garden” at Washington in 1865, (a highly unfavorable season for vines,) and in the Country Gentleman, January 25, 1866, asserts that they answer the purpose perfectly. The roof in this case was simply a board sixteen inches wide nailed to the top of the posts. In the Prairie Farmer for December 24, 1864, T. K. Phoenix writes: “It is a fact worthy of note that those vines under our covered trellis never had a mildewed leaf and had ripened their wood hard and fine, while exposed vines all went. So much in favor of protection, and such simple protection too!”

Finally, William Saunders, to whom we are indebted for the revival of this method, adds: “I have nearly one hundred varieties of grapes under the shelter trellis; as figured and described in the Agricultural Report for 1861, and none so sheltered showed any signs of mildew, although we lost very heavily on those not protected last summer,” (1864.) For a description and illustration of Saunders’s shelter trellis, see Patent Office Agricultural Report for 1861, pp. 497, 498.

Another method, which has effectually prevented the appearance of mildew, by enabling the vine to withstand the effects of excessive radiation by night, is to permit the vine to trail upon the ground. We have seen very fine crops of Concords at Hammonton, New Jersey, grown without a trellis or stake, but lying upon the ground, the fruit resting upon strips of cedar bark. These grapes were nearly all perfect, and received a premium as the best grapes in the New York market. Another grower in the same county of Atlantic, New Jersey, trained five hundred Concord vines on frames near the ground, so that the surface was protected from the sunshine by the foliage. No “rot” appeared on his vines thus treated, while in the immediate vicinity Concord vines tied to stakes suffered severely from “rot.” Again: the most careful cultivators at Hammondsport, Steuben county, New York, train their vines upon the low trellis in such a manner that the bunches of grapes will be near to the soil, and receive the warmth radiated from the surface; thereby insuring early maturity, a richer flavor, more abundant saccharine, and higher aroma, than if grown at a greater distance from the ground. Thus grapes on branches hanging within a foot of the soil have been found fully ripe and rich in bouquet, while those three feet higher were still unripe and extremely acid.  This method of training, combined with Lawrence’s shelters, but four feet from the soil, would seem to leave little to desire as requisite to safety of the leaf in summer, and perfect maturation of the grape.

As there are many localities where, from the nature of the soil, the grapes would be injured by close proximity to the earth, we would suggest that a trellis, with uprights so hinged to their foundation posts as to permit their depression in sections towards, or almost in contact with, the surface of the ground, might prove valuable. On occasions when a cold night is prognosticated by the psychrometer, by laying this trellis and its attached vines nearly horizontal, we could place them in a stratum of the atmosphere the warmest, the most humid, and, consequently, the least exposed to the evils of excessive radiation, which the overlapping leaves would in some measure also arrest. At other times when, by day, a rapidly drying circulation of air may be deemed necessary, or during a damp period, the trellis and its vines could be raised and fastened vertically, as desired. It is highly probable that, by combining the low horizontal trellis, properly sheltered, with the hinged posts depressible at will, we could avoid much of the injury we now suffer from both mildew and “rot.”

ON THE ROT OF THE GRAPE AND REMEDIES THEREFOR.

The introduction of many new varieties of vines, supposed to promise better than the old, and render grape-growing generally profitable, has brought into the horticultural ranks many intelligent and educated amateurs. The keen interest with which these scrutinize, study and reason, respecting pomological practices and phenomena, while untrammelled by venerable routine, is refreshing, and cannot fail to upset many old notions and to develop many truths hitherto overlooked.

Among the errors which a sound philosophy will dissipate may be named the following, with the reasons assigned for believing them erroneous, deduced from the physiology of the vine as taught by the botanists, but disregarded by the vigneron. The more important practical errors are deep trenching, high manuring with animal and vegetable matters, planting in heavy, undrained clays,6 an impervious sub-soil on low grounds with defective drainage in general, close pruning, and heavy cropping: The reason for believing the above practices hurtful are, that deep trenching causes the roots to run deep, and high manuring induces a rampant growth of wood and root; the heavy clays do not permit a ready passage of rain and air, and an impervious sub-soil retains the heavy rains around their abundant roots with their multitudes of feeders and moisture imbibers. The superabundant water from heavy rains being generally followed, in early summer, by excessive atmospheric heat and very high temperatures in some soils, which is retained during the night, the vine is stimulated to vigorous action, and draws up from the saturated earth more moisture than it can evaporate through the sparse foliage which close pruning has permitted to develop.  An engorgement of the tissues of the leaf and young fruits the consequence, and rupture and death of the fruit, known as the “rot” and blight of the leaf, which prepares for the fungous growth known as “mildew.”

Added to the above causes of decay of the vine may be cited the practice of taking from it, occasionally, (or it may be successive,) heavy crops in favorable years. From two to three times as much fruit is retained as the vines should be permitted to carry, which excess so impoverishes and weakens the plant as to render it incapable of resisting any of the causes of injury to which it is exposed, even when but of moderate amount. Vines which, in many instances, might have continued moderately productive, are thus destroyed, and a continued demand sustained for “new varieties which will not rot nor mildew” to take their places, to receive the same treatment and to meet the same fate.

A cultivator of many years’ experience near the Hudson river, New York, says, that after having qualified himself, as he thought, for the business of grape-growing, it required four or five years to bring his Isabellas into bearing condition, and five years more to unlearn what he had learned. Having almost killed his vines by pursuing the close-pruning system and summer trimming, as recommended by gardeners whose knowledge had been derived from experience in the plant-propagating house, he was obliged to reform his method, and now pursues that so successful in the hands of Dr. Underhill, of Croton Point vineyards. The same grape-grower adds, that excessive bearing is a great error, and that the worst cultivator always obtains the largest crops while his vines last, and that a small uniform crop every year is indicative of good cultivation, and recommends that but five or six pounds of fruit be permitted to mature on each Isabella vine occupying a space of eight by ten feet.

In the New York semi-weekly Tribune, August 30, and October 17, 1865, is recorded the experience of E. G. Johnson, of Peoria, Illinois, which is pertinent. He says that in the black prairie soil, on clayey sub-soil, “rot and mildew.” prevail, and that vines thoroughly pruned and tied to stakes rotted badly, while those which were unpruned on high trellises escaped. An amateur, residing near, always lost his Catawbas when he cut his vines; but having stopped “stopping” them for some years past, has had no “rot” since. Finally, that he had found six cases of Catawba vines in his vicinity where the grapes did not rot, nor the vines mildew; and that in each case the vines had not been cut or pruned, and that he knew of no case where pruned vines did not rot or mildew.

Dr. Warder says that the Catawbas around Cincinnati “have so degenerated that this year (1865) the vines are nearly barren.” To what cause can this be ascribed, save neglect of the natural conditions of equilibrium between the roots and leaves, enfeebling of the plant from year to year, by rushing the juices into fruit, instead of dividing them in due proportion to the demands of the plant and a fair crop, with occasional severe ordeals of high atmospheric humidity on an ungenial soil, and alternating extremes of dryness during the growing season, which their enfeebled condition cannot endure?

We must learn from nature, “the kindest mother of us all,” if we would learn aright. The vine, we all know, is a climbing plant, destined to rise by help of other trees, and to grow in their partial shade, sheltered from the hot noonday sun, and protected from the extremest cold by night. We cannot change its nature, but must adapt our culture to its imperative necessities. How can we reasonably expect it to thrive through many seasons where it is deprived of shelter around or above, clipped into rigid stocks, and thwarted in every direction in which its instincts prompt it to extend, enfeebled and rendered the easy prey to atmospheric changes in every district not provided by nature with countervailing advantages?

A remedy for the prevention of the “rot,” where vines are already planted in deep-trenched, highly manured, tenacious, and retentive soils, has been proposed, and appears to be philosophical and highly promising. It is that of Dr. Schröder, the enthusiastic vineyardist, of Bloomington, Illinois. He remarks, as is generally observed, that the first crop of Catawbas is not injured by the rot, and therefore proposes that the vineyard shall be frequently renewed by layering, after each new vine thus formed shall have borne its first large crop, or the third or fourth year after planting. Long canes should be grown for layering and laid on the soil, extending to mid-way between the rows. By continuing this process successively from each new vine for four years, and extending the layers properly, the last plant may be brought in position to take the place of the original parent, and a vineyard of young vines be constantly maintained, which, it is claimed, are always vigorous, free from disease, and produce superior fruit.

This method, which appears well worthy of trial, certainly does away with the evil of extraordinary root extension and unnatural diminution of leaves, (or the evaporating organs,) by excessive pruning. We know that in the vine, as in other plants, the growth of the root and its branches keeps pace with the extension of the stem. As the latter shoots upwards and expands its leaves, the former grow outward, absorbing moisture to supply the evaporation into the air. he older the vines the greater must the root expansion have become, and the more numerous the rootlets occupied in absorption; but the annual pruning at one fell stroke destroys the equilibrium which nature had endeavored to establish, and the leaves and fruit of the aged pruned vine are rendered liable to engorgement and suffocation with excess of moisture or of sap.

GENERAL REMARKS ON MILDEW.

Frequent reference has been made to mildew, and some explanation of the meaning of the term and notice of our present knowledge of this evil may be here in place.

Fungi are an extensive family of cryptogamous plants, generally known as mushrooms, toad-stools, rust, smut, mould, mildews, etc. They are generally parasitic, or grow upon and derive their nourishment either entirely or in part from the substances they infest. They are found wherever there is decaying vegetation upon which to feed, and sometimes prey upon living tissues. Nothing of vegetable origin is free from their ravages, when exposed to influences favorable, to their growth. They are found also on animal dejections, on insects, whose death they cause, on the human skin, and even on bare stones, on iron but a few hours removed from the forge, and on acid chemical solutions. Our house-flies are often destroyed by a mould which, growing between the segments of their bodies, produces the white rings thereon, as many may have seen. Some cutaneous disorders are the result of the operations of these vegetable parasites. Oïdium albicans forms the disease called apthœ on the mucous membrane on the tongues of infants, penetrating so deeply as to be irremovable by art. It is found also in the nose, the wind-pipe, stomach and intestines.7 Fungi are an attendant of diphtheria; and are present in cholera vomitus as well as in yellow fever. Other parasites not much dissimilar abound in the scalp, causing diseases, others on the teeth, some on the respiratory organs of birds, in their brains and eggs, and they have even been observed in the midst of the human eye. Fish are often covered with them; the silk-worm has been destroyed by the Botrytis bassiane, and the “potato-rot” is now ascribed to the Botrytis infestans, both forms of fungous growth.

Prof. J. H. Salisbury has shown that the cause of “fever and ague” is no longer involved in mystery. He has not only detected, figured and described with minute accuracy the species of fungus which produces this disease but has propagated and cultivatd the plant within doors to an extent sufficient, to contaminate the atmosphere of the apartment and induce attacks of fever among its inmates. His labors also demonstrate that measles are of cryptogamous or fungous growth. (See Ohio Agricultural Report, for 1863, and American Journal of Medical Sciences, January, .1866.) These microscopic vegetable growths are probably also the predisposing cause of variola and small-pox, of the cholera and the rinderpest, and of the plague of olden time.8 Their dwelling-place is as universal as their growth is simple; the air we breathe contains them, and the winds waft their seminal spores from pole to pole. They attack the housekeeper’s bread and cheese, her preserves, her paste, her ink and her linen.9 Her yeast consists of a living organism which is among the lowest of the fungi, and there seems to be abundant experimental proof that the various kinds of fermentations, acetous, vinous, lactic, &c., are due to different kinds of organisms, or different generations of the same species, all of which are fungi.  Their attacks are not confined to the seeming dead forms of matter, but they play havoc with our fruits, (as the peach, the pear, the plum,) and attack remorselessly the foreign gooseberry, and both the foreign and the native vine and grape.

No class of organized structures is so little known, and the study of fungi is among the most recondite of pursuits. This arises from their microscopic character, their strange growths, the variety of forms through which they pass, baffling the researches of the closest observers. But enough is now known to show that they are perfect plants, growing from and producing bodies analogous to seeds; that a single plant produces millions of spores, or reproductive bodies, which are so small that they float upon the air scarcely affected by gravity; that they remain for an indefinite period inert, and are called into sudden vitality by atmospheric changes favorable to their germination; and that their sudden appearance can be readily explained to be due to natural causes, obscure only because unseen. They have been traced through their changes from the infinitesimally small spore to the perfect plant; hence they are not the result of spontaneous generation, as has been imagined by some, though it would seem scarcely possible tor any intelligent person to conceive such an origin.

The earliest vegetation of these obscure creations is a prolongation of the membrane of the spores or seminal dust, and not properly seeds, because merely individual cells. From these proceeds a’delicate, minute, webby growth called the mycclium, the true vegetation of the plant, and from this arises the reproductive bodies on which are formed the spores for future growth. It is this mycelium or close-growing mould which penetrates and destroys the object on which it is parasitic, or has fastened itself. Its fibres are so minute as to readily traverse the tissue or substance of the plant, and even the pores of solid wood, as may be seen in the “dry rot.” The spores produced from this mycelium are so minute as to appear like a cloud of impalpable dust. And when we consider how readily germs so minute and almost omnipresent, may be drawn up with the fluids which enter through the roots, or may be received directly through the breathing pores or plants, and remember that their office is to prey upon vegetable substances which are decaying, or have received a check through untoward atmospheric influences, we may be prepared to comprehend how they may suddenly appear over widely distant regions, and commit ravages so appalling.

So little is really known of the relations which these plants bear to each other, the transformatious they undergo, or the seeming transmigrations from one form to another, under change of conditions, &c., that a wide field of inquiry is here open to the young and assiduous microscopist. When we state that the fungus, producing fermentation in yeast, (or the true yeast itself,) will grow upon the diseased scalp of a scrofulous patient, take root, and exist for years without check by the medical treatment attempted; that the fungus from the “ringworm,” a disease of the skin, has been successfully used to produce fermentation (and that nearly as briskly as healthy yeast) when added to a barley wort;10 and finally, that forms of fungi considered distinct species cannot be distinguished from each other, or from yeast, but that their differences seem to be entirely dependent upon the kind of plant, or the diseased animal tissue on which the spores may chance to alight, we may well believe that much remains to be learned before the naturalist will be prepared to fix the place in his system of even the common mildew of our vines and grapes, Accordingly, the best informed mycologists have not determined to what undoubted genus our vine mildew belongs. Minds of the first class are, however, zealously engaged at present in the elucidation of the structure, and in determining the laws which govern these minute and mysterious organisms.

To discover the causes of mildew and rot has exercised the ingenuity of many inquirers. Some believe they have certainly found them in deep trenching, abounding humus, and retentive soils and sub-soils; all of which are highly injurious in seasons of great atmospheric humidity, and conducive to the production of the “rot.” Others assume that the cause of the rot is also the cause of the mildew, because they appear about the same time; but we believe without good reason. Both these evils no doubt arise from some derangement affecting the normal functions of the vine—some departure from the conditions of heat and moisture, either in the air or in the soil, which are absolutely demanded for its healthy growth and the maturation of the fruit. This must be self-evident, while it should also be equally clear that these conditions of temperatures and humidity, abnormal or excessive, are aggravated or rendered more injurious by the qualities of soil or position—by some esteemed the direct and specific cause of these evils. A cause for the sudden and wide-spread advent of the mildew on our grape leaves and fruit must be found as wide in its operation as is the resultant evil consequence; and must, therefore, be climatic, and climatic only. The outline sketch of the meteorological changes which preceded and accompanied this evil, and the freedom from its extreme effects in localities near wide waters, where these excessive changes of temperature and dryness were especially modified, point to the atmosphere and its fluctuating conditions as the controlling cause of the derangement which prepares for the growth of the fungi spores.

Some may still believe we have not found this cause in the cold nights resulting from extreme dryness, and the hot days following immediately thereafter, because the leaves of the vine were not frozen, nor even appeared to be injured in every ease. In reply, we may say that the extreme low temperatures, followed by extreme high heats, accompanied by excessive dryness, are all conditions highly favorable to the development of the spores of the mildew, which feed upon disorganized tissues; and that freezing is not necessary to prepare for decay, may be learned from the following passage from our highest authority in physiological botany. A. de Candolle asserts, that “cold does not kill vegetation by a mechanical action proceeding from congelation of the fluids of vegetables, as some naturalists pretend, We recognize rather a physiological action in this change, for the vitality of the tissue is destroyed by a certain degree of cold, followed by a certain degree of heat, according to the peculiar nature of the plant. In the same manner as the gangrene which follows the thawing of a frozen part causes the death of an animal tissue, so the change or putrefaction which follows on rapid thawing will be the principal cause of the death of the vegetable tissue.  This is illustrated by the immediate death of hot-house plants when exposed to a temperature several degrees above freezing.” Herein lies the philosophy of the change in the tissue of the leaves exposed to intense radiation through dry air at night, followed by intense heats at mid-day in the same drying atmosphere.  The minute vessels are ruptured or dried up, and disorganized, so that decay is induced, and the ever-present spores of the fungus at once find a nidus in the decaying matter, for the removal of which they were created, take root, penetrate the leaves, or enwrap the berries, feeding upon the former and choking the latter, and destroying the remaining vitality of both by their rapid expansion and fatal folds.

OZONE AND THE VINE-MILDEW.

There are other atmospheric conditions, resultants of extreme dryness, or extreme humidity, or unusual cold, which indirectly affect the vine, and aid the development of fungous growth. It has been suggested that the relative amount of ozone in the air, which may be a peculiar form of oxygen, (or a component of this gas, if it be compound,) may exert an influence in promoting or preventing the appearance of the fungi on our vines and on other plants Though much remains to be learned respecting the development and character of this mysterious agent, we already know the conditions most favorable to its production, as well as those inimical to its appearance, or at least to the active exhibition of its energies. We know that chemical action increases with increase of heat and diminishes with reduction of temperature, and that ozone is less prevalent in the air during frosty weather. Moisture, to a certain amount, is favorable to chemical action, while an excess is-detrimental thereto; and though there is less ozone in the air when very dry, there is still less when it is very moist—a certain degree of humidity being favorable to its development and existence. Dr. Small wood, the meteorologist of Montreal, asserts that ozone is never present in dry air, and that the psychrometer will indicate its presence or absence. He adds, that east and south winds are ozonic at Montreal, and that northeast winds from off the land are not ozonic; also that westerly and northerly winds do not bear ozone with them, though sea breezes with mo:sture are strongly ozonic. These conditions are, however, modified in other latitudes, as we have observed repeatedly that winds from the N., NE., S.E., and S.W., may be strongly ozonic at our station. Dr. Smallwood also has shown that there is a connexion between the amount of ozone in the air and the health of a district. Thus, during the prevalence of cholera the amount of ozone is least, and the humidity was at the same time diminished. Dr, Moffatt has concluded, from the results of a large number of experiments in England, that ozone plays an important part in controlling or preventing epidemics, generally by removing the cause prevailing in the infected air of a district. Finally, C. Kosman has ascertained at Strasburg, France, that the green portions of all plants exhale ozone, the result of the chemical changes going on at the surface, or in the vessels of the leaf.

The origin of infectious diseases prevailing over wide districts has, in some instances, been shown to be due to the presence of minute fungi, or rather to their germs or spores, which are ever ready to take hold and grow in favorable positions and conditions; and we know that our grape-vines are sufferers from causes having many points of analogy with the above. Now, when we consider that the appearance of mildew is invariably preceded by sudden changes in the atmospheric moisture or dryness, heat and cold; that excessively moist air as well as excessively dry air are both unfavorable to the presence of ozone, which acts so energetically in the destruction of fungi; that plants, when in health, give out ozone, and thus protect themselves from the devouring enemy ever ready to pounce upon the unprotected organism, we need not wonder that, during our oppressively moist days and unseasonably cold nights, the chemical changes connected with (or themselves the sources of) the vitality of the plant should be subdued or oppressed, the quantity of ozone in the air and on the leaf be diminished, and the torpid condition of the leaf render it an easy prey to the invisible but omnipresent enemy, and universal mildew be the result.

NOTES & FOOTNOTES

1. The evaporation must depend on the nature of the surface, and a smaller amount of vapor is produced in a given time from a given surface of moist earth than from water, and in a calm than in a current of air. The experiments of Gasparin, in France, indicate that the evaporation from the moist earth may be, at certain seasons, from one-tenth to one-sixth of that from water. The experiments of Mr. Williams show that land covered with trees or vegetables emits more vapor than the same space covered with water, even to the amount of one-third more.

2.  Ellet on the Mississippi and Ohio rivers.

3.  A correspondent in northern Illinois writes: “I am situated on high open prairie about nine hundred feet above tide-water, and about six miles from woods or timber on the north, south, and east, while on the southwest and west is a prairie open to the Mississippi, one hundred miles distant. Our winds have free course, disturbed by no local influence, but truly go it with a rush. The force of the winds is rarely reduced to 0 or calm, but is frequently 5 to 6, at times 7 to 8, of the Smithsonian scale, which indicate a high wind to a gale, and even a violent gale. These winds from the southwest are often dry, and are sometimes so arid that in their sweep over the soil vegetation is withered before them as if at the touch of fire.”

4.  As extreme variations from high mid-day heat to unseasonable cold, on the verge of frost, are evidently accompanied by, if not dependent upon, extreme atmospheric dryness, an instrument that will readily show the conditions of deficient moisture, may foretell the coming cold, and thus enable the gardener, by being forewarned, to be forearmed. The wet and dry bulb thermometer or psychrometer will often foretell, at 2 p. m. of the day before, that an extreme low temperature will probably result before dawn of the following day. The low humidity detected by the psychrometer thus often becomes a good prognosticator of frost. It is true that a change in the wind. the amount of cloudiness, &c., by increasing the proportion of vapor during the night, or bringing in warmer currents, may happily disappoint these prognostics at times. Still the gardener who daily observes the psychrometer aright, and consults the tables prepared to save calculation, or makes use of a “vapor index” (which is quite easily inspected, and dispenses with tables, ) will, during the growing season, find its prognostics very valuable and may save many a tender plant.
"Lippincott’s vapor index” is a very convenient card with rotating index, by which, from the observed temperatures of the wet and dry bulb thermometers, the most unskilled person may easily determine in a few seconds the actual relative-humidity or percentage of vapor in the air. It is sold at a moderate price, and may be had on application to James W. Queen & Co., opticians and dealers in philosophical instruments, 924 Chestnut street, Philadelphia.
The psychrometer and vapor index become also most valuable aids to the barometer, as foretellers of a change in the weather; indeed, it is now well ascertained that without a psychrometer the prognostics of a barometer are frequently fallacious, and that simultaneous observations of these two instruments most usefully correct each other’s indications.
The rules for foretelling a change in the weather by means of the barometer and psychrometer are few and simple. Our own observations show that, as a general rule, a storm can occur only after a rise in. the barometer followed by a fall, and accompanied by increased relative-humidity approaching to saturation, heavy clouding gathered from the southwest, while the surface wind is from the northeast or from the southeast. Let the changes in the barometer be what they may, if the relative-humidity be not near or at saturation, no rain can fall; and so reliable do we find these indications of the psychrometer when interpreted by the "vapor index,” that we may oftentimes disregard the barometer, the other prognostics being favorable to a change. Thus one may not be at a loss for a weather-gauge with these simple instruments at hand, even though his barometer be found in the predicament of Sir William Hamilton’s village hostess, who, he relates, was afraid the weather-glass was not exactly right, for all the quicksilver had run out of it.
For the economical convenience of those who cannot readily obtain psychrometers, because distant from the large cities, we may state that any two good thermometers, if they can be found in the country stores, and if closely alike in their range, size of bulb and bore, may be employed as a psychrometer, by covering the bulb of one of them with thin muslin, wet ting this at the time of observation, and then subjecting them both to a moderate swinging until the mercury in each ceases to fall. A reference to the "vapor index” will then inform the observer how much vapor is present. All common thermometers are erroneous to the amount of one to three degrees, and should be corrected by immersion in melting ice for 32 degrees, or compared with an undoubted standard, and the tube shifted upon the index to the true degree.
The Smithsonian Institution should invite its corps of observers to add the psychrometer to their list of meteorological instruments. More extensive observations of the fall of rain and snow are also desired. The number now reporting observations made with the psychrometer is limited, and we hope our remarks on the effects of drought and the influences of humidity, excessive or deficient, will stimulate many to use the instrument by which the important phenomena referred to may be accurately determined and recorded.
The philosophy of the methods of determining the amount of vapor in tho air may be seen in the Patent Office Report for 1858, article Meteorology, and should be read by all interested in this branch of the subject.

5.  Also, Isaiah, xiv, 8.

6.  Heavy clays where the surface drainage is good and the surrounding climatic conditions eminently favorable, may prove more productive of fruit of superior excellence and less susceptible to mildew than some sandy loams abounding in vegetable matter and partially underdrained. This may arise from the more ready absorption of water and the higher heat attained by the latter soil in early summer, when the heaviest rain-fall is often followed by very high temperatures which face the vines into excessive action; while the clay soil, with good surface drainage, will neither absorb water so rapidly nor become so quickly heated by day, nor so readily cooled by night. The mildew observed on the shores of Lake Erie appeared on land abounding in sand and vegetable matter.

Dr. Laycock and others regard diphtheria as due to the Oïdium albicans whose sporules and mycelium have been found on the mucous membrane of the mouth, fauces, etc. Diphtheria is most common in the foul districts of France and England, and is attributed to the action of putrid effluvia on the fauces, especially the foul air of sewers and cesspools, which offer highly favorable conditions for the propagation of fungi. Vitray and Desmartis are of opinion that there is no distinction between the Oïdium albicans and Oïdium Tuckeri, the former causing the diphtheria, the latter the European vine mildew. A connexion between the appearance of the European vine-mildew and the various forms of epidemic laryngeal maladies has been observed, which strengthens this presumption, the spread of tho former having been followed by that of the latter.
Rev. Mr. Berkeley, one of the highest authorities on fungi, says that the mould so extremely common in England on pears, apples, and other fruits in autumn, and frequently, while yet hanging on the tree, is the Oïdium fructigenum, which is another species of the genus to which that causing diphtheria belongs. He also asserts that the Isabella has never suffered from the mildew when grown in Europe, though the Oïdium Tuckeri destroyed the European vines generally, from England to Madeira.
Many of these conclusions we believe to be unwarranted assumptions, so much remains to bo learned respecting the classification of fungi. The vine-mildew of our native vines is not the Oïdium Tuckeri, and even this is now shown to be but a barren form of another genus, known as Erysiphe.

8.  The theory of the "cryptogamous origin of malarious and epidemic fevers” was broached by Dr. John K. Mitchell, of Philadelphia, upwards of twenty years ago, as will be seen on consulting his lectures bearing the above title, and republished in five essays in 1859.  These lectures abound in facts of interest and value.

9.  Dr. Forry relates that, in Florida, he had known fungi to spring up in a night and to incorporate themselves with a woollen garment so inextricably as to render separation impracticable.

10.  Journal of Microscopic Science. January 7. 1866.