one may multiply the duration of sunshine by the percentage of observed clearness and obtain the duration of sunshine for a special station. But this will give us a value that is greater or less than the value of the true intensity of sunshine according as the cloudiness occurs mostly in the morning and evening or in the midday hours. The only method for obtaining a satisfactory value of the intensity of radiation as coming direct from the sun or as reflected from the sky, the clouds, and the earth, is to maintain a self-registering actinometer or, in place of that, frequent daily observations. In these tables I have adopted the division of each month into three parts, as done by Libbey and occasionally used by meteorologists, but the system of pentades, used by Dove, is often preferable; however, this present system is convenient for monthly summations, and is also used in the climatic table of Section II.a Sums total of possible duration of sunshine, in hours, from January 1 up to any day of the year. January 1-10 10 106.7 105.4 104.0 January 11-20 10 214.5 212.0 January 21-31 11 334.7 331.0 February 1-10 . 10 446.0 February 11-20. 10 559.4 309.5 414.9 523.7 February 21-28. 102.5 101.0 99.4 97.7 209.3 206.4 203.5 200.4 197.2 327.1 322.9 318.7 314.2 441.4 436.6 431.4 426.2 420.6 554.1 548.6 542.6 536.7 530.2 645.2 640.3 633.9 627.6 €20.6 613.6 762.4 757.2 750.5 743.8 736.4 729.0 882.1 876.8 870.0 863.2 855.7 848.2 11 1,021.7 1,016. 8 1,011.7 1,005.0 998.4 991.1 983.7 10 1,146. 4 1, 141.9 1,137.2 1,130.9 1,124.7 1,117.9 1,110.9 10 1,273.3 1,269.4 1,265.3 1,259.71, 254.2 1,248.1 1,241.8 10 1,402.3 1,399.2 1,396.0 1,391.3 1,386.7 1,381.5 1,376.2 10 1,533.3 1,531.2 1,529.0 1,525.4 1,521.9 1,517.9 1,513.8 10 1,666.0 1,665.1 1,664.1 1,661.8 1,659.6 1,657.0 1,654.3 11 1,813.6 1,814.1 1,814.6 1,813.8 1,813.2 1,812.4 1,811.4 10 1,948.8 1,950.7 1,952.7 1,953.4 1,954.4 1,955.3 1,956.0 10 2,084.5 2,087.9 2,091.4 2,093.7 2,096.3 2,099.0 2,101.5 10 2,220.2 2,225.1 2,230.1 2,234.0 2,238.2 2,242.7 2,247.0 10 2,355.4 2,361.7 2,368.2 2.373.6 2,379.4 2,385.6 2,391.6 10 2,489.7 2,497.3 2,505.2 2,512.0 2,519.3 2,527.1 2,534.7 11 2,636.0 2,644.9 2,654.1 2,662.3 2,671.0 2,680.4 2,689.6 10 2,767.1 2,777.1 2,787.3 2,796.6 2,806.4 2,817.0 2,827.5 10 2,896.3 2,907.1 2,918.1 2,928.3 2,939.0 2,950.6 2,962.1 11 3,036.1 3,047.5 3,059.2 3,070.2 3,081.7 3,094.1 3,106.4 10 3,160.8 3,172.6 3, 184.7 3, 196.1 10 3,283.2 3,295.2 3,307.4 3,319.0 10 3,403.3 3,415. 23, 427.43,439.0 3,451.0 3,464.0 3,476.9 10 3,521.1 3,532.7 3,544.6 3,555.9 3,567.6 3,580.2 3,592.8 10 3,636.6 3,647.7 3,659.1 3,669.9 3, 681.0 3,693.0 3,705.0 11 3,761.2 3,771.5 3,782.1 3,792.1 3,802.3 3,813.4 3,824.5 10 3,872.3 3,881.73, 891.3 3,900.3 3,909.4 3,919.4 3,929.4 a Omitted. 3,208.0 3,220.9 3,233.6 3,331.1 3,344.2 3,357.1 Sum total of possible duration of sunshine, in hours, from January 1 up to any day of the year-Continued. November 11-20. December 1-10 December 11-20 December 21-31 For leap year add to all numbers after February 28 January 1-December 31, 1905 11 Hours. Hours. Hours. Hours. Hours. Hours. Hours. 10 3,981.5 3,989.8 3,999.3 4,006.1 4,014.0 4,022.7 4,031.4 10 4,089.3 4,096. 24, 104.3 4, 109.9 4, 116.5 4,123.7 4,130.9 10 4, 196.0 4,201.6 4,208.3 4, 212.4 4,217.5 4,223.1 4, 228.6 10 4,302.2 4,306.4 4,311.6 4,314.1 4,317.6 4,321.5 4,325.3 4,418.9 4,421.5 4,425.1 4, 425.9 4,427.7 4,429.7 4 431.6 March 11-20 10 839.8 831.8 822.6 March 21-31 April 1-10. 11 April 11-20. May 11-20. May 21-31. June 21-30 July 11-20. July 21-31. August 1-10 August 11-20 August 21-31 September 1-10 October 11-20. October 21-31. November 1-10. December 1-10 For leap year add to all num- 813.0 802.4 791.0 778.7 975.4 967.6 958.7 949.3 938.9 927.8 915.9 10 1,103.2 1,095.9 1,087.5 1,078.7 1,062.0 1,058.6 1,047.5 1,966.3 2,129.1 11 2,700.1 2,711.2 2,725.1 2,735.8 2,79.6 2,764.7 2,782.0 10 2,839.3 2,851.7 2,867.1 2,879.4 2,894.9 2,911.9 2,931.3 10 2,975.0 2,988.5 3,005. 1 3,018.8 3,035.7 3,054.2 3,075.2 11 3,120.2 3,134.7 3, 152.3 3,167.0 3,185.0 3,204.8 3,227.2 10 3,248.0 3,263.0 3,281.1 3,296.5 3,315.1 3,335.6 3,358.8 10 3,371.8 3,387.0 3,405.3 3,421.0 3,439.9 3, 460.7 3,484.2 10 3,491.53,506.6 3,524.9 3,540.5 3,559.3 3,570.0 3,603.4 10 3,607.1 3,621.8 3,639.7 3,654.9 3,673.3 3,693.5 3,716.4 10 3,718.7 3,732.7 3,749.9 3, 764.4 3,782.0 3,801.3 3,823.2 11 3,837.2 3,850.2 3,866.3 3,879.6 3,895.9 3,913.7 3,934.2 10 3,940.9 3,952.7 3,967.5 3,979.3 3,994.1 4,010.2 4,028.9 10 4,041.4 4,051.7 4,064.8 4,074.9 4,087.9 4,101.9 4, 118.3 10 4,139.2 4,147.8 4, 159.0 4,167.1 4, 178.0 4, 189.6 4, 203.5 10 4,235.0 4, 241.8 4, 251.04, 256.9 4,265.3 4, 274.4 4,285.5 10 4,329.8 4,334.7 4,341.7 4,345.3 4,351.2 4,357.6 4,365.7 11 4,434.0 4,436.8 4, 441.4 4, 442.5 4,445.7 4,449.0 4,453.8 Chapter VI. MOISTURE OF THE SOIL. IN GENERAL. The soil receives its water supply either by natural rainfall or by irrigation. The plant in successive generations of cultivation adapts itself to the ordinary supply of water, but in order to perpetuate its kind it must have sufficient during the growing season to serve it as a medium for extracting from the soil and air the nutritious substances needed by it for its own development. The water really available to the plant is principally that which is left in the soil close to the roots after the surface drainage has carried off a large per cent of the original rainfall and after the evaporation by the dry wind has taken 20 per cent of the remainder from the surface soil and after a further large per cent of the remainder has by percolation or seepage slowly settled down beyond the reach of the roots of the plant. Thus it happens that the roots rarely have left for their use 20 per cent of the original rainfall, and this is the so-called "useful remainder." Generally this remainder is best expressed as a percentage of what the soil would hold were it completely saturated. Therefore its absolute quantity will vary with the character of different soils EVAPORATION FROM THE SURFACE OF FRESH WATER. MONTSOURIS DATA FROM DESCROIX. An approximate idea of the relation between the velocity of the wind, its temperature, and its dryness, on the one hand, and its power to evaporate water on the other, may be obtained by collating the data given by Descroix in his article on "The climatology of Paris," in the Montsouris Annuaire, 1890, page 121. From the mass of data given by him I select the averages taken according to the direction of the wind, or wind roses, for the three summer months June, July, and August, 1889, as these are the months during which crops are liable to suffer the most severely from droughts and dry winds. I give them in the following table: We see that the driest winds, or those whose relative humidity is small, such as the north and east winds, give a large evaporation, and that the velocity and temperature of the west winds, which are a little less than those of the southwest winds, does not compensate for the dryness, which latter enables them to evaporate a little less than the southwest winds. By multiplying the average daily evaporation by the number of days we obtain the total evaporation from the saturated paper of the Piche instrument. This exceeds the total rainfall, but we are not to infer that the evaporation from ground and leaves must also necessarily exceed the rainfall, although this is generally true for the sum mer season. BOSTON DATA FROM E. J. FITZGERALD. The evaporation of the water from leaves and from the ground depends upon the temperature, wind, and humidity of the air. It is a rather complex result; if the above-mentioned elements remain constant for any time at the surface of the mass of water the evaporation from that surface will be closely represented by the following formula which is due to Fitzgerald, of Boston, E=0.0166 (P-p) (1+4 W), where W is the velocity of the wind in miles per hour; P the tension of vapor in inches of mercury corresponding to the temperature of the water; p is the tension of vapor corresponding to the dew point in the free air; E is the evaporation expressed in inches of depth of water evaporated per hour under atmospheric pressure between 29 and 31 inches of the barometer. The evaporation from leaves and soils is usually less than that from water about in the proportion in which the soil approximates its state of maximum saturation, or in proportion as the leaf can transpire moisture through its cell walls. Therefore any observations of evaporation that we may make for comparative purposes can give us only the relative evaporating power of the wind and not the absolute evaporation from plants and soils. THE PICHE EVAPORIMETER. The simplest apparatus for observing evaporation is that known as the Piche evaporimeter. This consists of a glass tube closed at the top and hung in a free exposure; the tube is less than half an inch in diameter and filled with water; its lower open end is closed by a horizontal disk of bibulous paper about twice the diameter of the tube; the water evaporated from this paper is supplied from within the tube. The observer has simply to read the height of the water in the tube as it slowly descends hour by hour. The number so read off is easily converted into one that expresses the depth of water evaporated per hour from unit surface. The following table from Montsouris Annuaire, 1888, page 254, shows the average evaporation thus determined by an instrument placed in the shade, also the corresponding temperatures and other data, as observed at Montsouris during thirteen years. Prof. Thomas Russell, of the Signal Office, has published results of some observations on the effect of the wind on the evaporation from the disks of the Piche evaporimeter. (See Annual Report Chief Signal Officer, 1888, p. 176, or Monthly Weather Review, 1888, |