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necessary to accomplish this, and that, too, to a greater degree if the soil be covered with vegetation. The phenomena of autumn generally resemble closely those of summer.

(23) In general the fluctuations in the temperature of the earth are not less dependent on the precipitation than on the variations in the temperature of the air.

SOIL TEMPERATURES AS AFFECTED BY SURFACE SLOPE AND COVERING (WOLLNY).

In reference to the effect of the slope of the earth's surface on the temperature of the soil, Wollny (1888, p. 364) has made an extensive series of measurements at Munich from which he draws the following conclusions in continuation of those published by him in 1883. His temperatures were measured bihourly at a depth of 15 centimeters under both fallow soil and grass sod; the differences referred to amounted to 3° and 4° F. in individual cases, but on the average to scarcely 1° F.

(1) That soil whose exposure is toward the south is the warmest, then comes the east, then the west, and finally the north exposure.

(2) The southern exposure is warmer in proportion as the inclination to the horizon is greater.

(3) The difference of temperature between the north and south exposure is much greater than between east and west.

(4) The difference in the warming of the soil for north and south exposures is greater in proportion as the surfaces have a greater inclination.

Wollny (1888, p. 415) has also investigated the influence of the covering of straw and chaff on the temperature and moisture of the soil. He finds the following conclusions:

(1) That at a depth of 10 centimeters the naked soil is warmed. more with rising air temperatures and is cooled more with falling air temperatures than under any one of the different forms of straw covering.

(2) That the variations in the temperature within the straw litter are very much less than in the earth.

(3) That the earth is in general somewhat colder than the material of which the litter is made, except when the latter is moss.

(4) That among the various materials forming a litter the pine. needles are warmed the most, the oak leaves and the fir-tree needles are less warm, while the litter of moss is the coldest.

The different temperatures observed were as follows, on the average of the months April to September: Pine needles, 16.93° C.; oak leaves, 16.62° C.; fir needles, 16.34° C.; the naked soil at a depth of 10 centimeters, 16.18° C.; moss, 15.95° C.

The difference between the morning and evening temperatures shows:

(1) That the cooling during the night and the warming during the day is appreciably larger for the naked earth than for the various kinds of litter.

(2) That the pine needles warm up most during the day and the moss warms up least; that the fir needles cool most during the night and the pine needles least.

The power of retaining moisture varies with the different kinds of litter as follows:

(1) Any litter of forest leaves or needles is moister than the earth, but the moss is less moist than the earth; the gradation is from oak leaves, the highest, through fir needles to moss, the lowest.

With regard to evaporation Wollny shows that the naked earth loses a greater quantity of moisture by evaporation than do the various kinds of litter.

(2) That the moss litter evaporates the most, but the litter of forest leaves the least.

(3) That the quantity of evaporation is greater the thinner the layer of the litter.

In general, then, the litters of leaves and of pine needles give up the rain water that falls upon them to the ground beneath in larger proportion, but still continue to be very moist because they lose, relatively, little water by evaporation; furthermore, that the moss litter is distinguished by large variations in its contained water because it has on the one hand a large capacity for water and on the other hand a very considerable evaporating power.

SOIL TEMPERATURES OBSERVED AT GREENWICH, ENGLAND. Among the limited number of long-continued series of observations of temperatures of soil near the surface is that maintained at Greenwich Observatory, England, since June, 1846. This series embraces observations at considerable depths that will not interest the student. of agriculture, but we reproduce in the following table the results of observations at 1 inch in depth, as given in the annual volumes of the Greenwich Observatory for 1878, and as given in J. D. Everett's memoir of 1860. These soil temperatures can be used in any subsequent study of English crops throughout the southern half of England or in analogous climates.

daily maximum air temperature. Rainfall lowers the temperature of the soil, as on March 18, 1890, at 8 inches depth by 2° F., but at 24 inches depth by 0.5° F. At 12 inches depth the soil was not frozen throughout the year, but at 8 inches it was frozen up to the 7th of March. The soil temperatures were read daily at 3 p. m.; the soil was naturally dry and light, and was covered with a thin grass. The thermometers were maximums and minimums, apparently read from above ground without being disturbed in their positions.

Observations at Pendleton, Oreg., in 1890.

[From the Monthly Reports of the Oregon State Weather Bureau.]

Jan. Feb. Mar. Apr. May. June. July. Aug. Sept. Oct. Nov.

Air temperature. Absolute maximum temperature.

Absolute minimum temper

ature..

Mean of maximum temperature..

Mean of minimum temperature...

Monthly mean temperature.

Precipitation.

Total monthly rainfall.

4-inch depth:

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al. 19 al. 52 02.04 0.17 al. 51 a1.80 0.08 0.07 0.27 0.63 0.01

Soil temperature.

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33.0 44.0 49.0 68.0 72.0 80.0 83.0 78.0 71.0 60.0 49.0 20.0 29.0 30.0 48.0 59.0 61.0 72.0 71.0 64.0 50.0 38.0 27.8 36.6 40.9 55.3 66.3 68.4 77.6 75.8 66.5 53.7 43.2

Maximum
Minimum
Mean.

12-inch depth:

Maximum
Minimum
Mean.

24-inch depth:

Maximum
Minimum

Mean.

34.0 41.0 46.0 62.0 67.0 71.0 78.0 85.0 70.0 63.0 51.0 27.0 33.0 33.0 46.0 58.0 60.0 69.0 71.0 64.0 51.0 40.0 30.4 37.1 39.8 52.2 63.1 65.8 45.2

73.7 73.3 65.7 54.7

38.0 40.0 45.0 58.0 64.0 66.0 74.0 73.0 70.0 64.0 54.0 33.0 35.0 36.0 45.0 58.0 61.0 68.0 71.0 64.0 54.0 44.0 34.6 38.1 40.1 50.1 60.9 63.7 30.7 71.7 66.7 57.3 48.5

a Inches.

SOIL TEMPERATURES OBSERVED AT MONTREAL, CANADA. As illustrating temperatures of the ground in a very cold locality, I quote the work of Messrs. C. H. McLeod and D. P. Penhallow, of McGill College Observatory, Montreal, who have maintained a series of observations of the temperature of the earth by Becquerel's method, in which the temperature of a coil of wire in the laboratory is brought to equality with the temperature of a similar coil buried in the

of the maximum temperatures of the air, less the temperatures of the soil at 2 p. m. at a depth of 2 inches was 2.3° F. in July, 1888, and 3° F. in August, 1888. On the other hand, the average value of the maximum temperature of the air, less the temperature of the soil at 2 p. m. at a depth of 12 inches was 12° F. for the observations here given, scattered through July and August, 1888.

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It would appear that the reading of the soil temperature is frequently omitted when rain falls; this is a bad practice, but the records suffice to show us that in this dry country and during the summer time the maximum surface temperatures of the soil will not differ much from the maximum temperatures of the air, while the soil temperatures at 12 inches will closely follow the mean temperature of the air. The latter mean, viz, one-half the sum of the maximum and minimum record for any day is greater than the mean temperature of the layers of soil at 2 and 12 inches depth, as observed at 2 p. m., by about 6° F.

SOIL TEMPERATURES OBSERVED AT AUBURN, ALA.

As an illustration of soil temperatures in a southern locality I have chosen the following record for 1889 at Auburn, Ala., where the agricultural experiment station has maintained three sets of buried thermometers, two of them in sandy soils on hills and one in moist bottom land near the banks of a small stream. It appears from these records that the difference in temperature in the growing season between the so-called "cold wet" and "warm dry" soils averages but a few degrees; in fact, I doubt whether it is appreciable from observations having the accuracy of those here given. Thus at 3 inches depth and during the warm half of the year the maximum temperatures on the hill average 1° F. above those in the bottom land, while the minimum temperatures on the hill average 2° F. colder than those of the bottom lands. The temperatures here given are the averages of the maxima and minima and are taken from successive monthly reports and from Bulletin No. 18 of the Alabama Agricultural Experiment Station. In these, as at most other United States stations, the correction for the temperature of the long stem of the thermometer still remains to be applied. A comparison of the temperature at 3 inches depth with the maximum and minimum air temperature shows that the soil is warmer than the air in the daytime from April to October, inclusive, and warmer than the air at the minimum temperatures throughout the year. This latter is true for the minimum temperatures of the soil down to a depth of 96 inches, but the excess of maxima temperatures of the soil over those of the air during the daytime in summer ceases a little below 6 inches. Evidently the temperature of the soil is sufficiently high to allow of the growth of some form of vegetation throughout the year.

Extremes and means of soil temperatures for 1889, as observed at Auburn, Ala. [Lat. 32°.6 N.; long. 85°.4 W.; altitude, 732 feet.]

Air temperatures. Mean air temperature.

Jan. Feb. Mar. Apr. May. June. July. Aug. Sept. Oct. Nov. Dec.

• F. • F. • F.

• F.
• F.
• F.
° F. 。 F.
70.1 76.1 80.7 77.6 74.8 62.3 53.1 57.8

• F. • F. • F. • F.
46.9 46.3 54.7 62.5

Mean radiation temper-
ature
Maximum air tempera-

39.7

ture

36.8 43.2 55.6
67.0 75.0 76.0 82.0 89.0

57.2

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diation temperature.. 51.0 66.5 54.0 62.0 63.0 Minimum terrestrial ra

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diation temperature.. 21.0 24.0 32.0 37.0 | 43.0 | 43.0 60.0

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