416 Action of the Atmosphere upon neichj-deepened Soil. 



J. Forbes found a coolness by evaporation, amounting' to 20^ F., 

 the thermometer in the shade bemg at 92° ; and Baron Humboldt, 

 in his journey in Asia, noticed a difference from the same cause, 

 amounting; to 21^ F., the temperature of the air being 74 .6. 

 i^Brit. Assoc. Report, 1832, p. 243.) The alternations of tem- 

 perature, therefore, to which the surface-soil is exposed are much 

 greater than would at first sight appear. Even in this country, 

 from 150^ in the sun to 15° below zero in the shade, we have an 

 occasional range of 165° F., being from 118° above the freezing 

 point of water to 46° below it. 



The following table by Mr. Robert Thompson gives the average 

 results of daily observations at Chiswick, near London, from 1826 

 to 1853:— 



In India the thermometer is said occasionally to range from 

 nearly zero, before sunrise, to 130^ F. at noon. (^Tliompsous 

 Meteorology, p. 55.) 



Such being the case with the surface, let us now see what takes 

 place below, that we may compai'e the conditions of the top soil 

 with those of that Avhich lies dead beneath the plougli furrow. 



To assist us here we have a very valuable set of observations 

 taken under the direction of Leslie, at Abbotshall, the seat of 

 Mr. Ferguson of Raith, about 50 feet above the sea level, and 

 near a mile from the shore of Kirkaldy, in Scotland, during 

 1815, 1816, and 1817. The details will be found in Leslie's 

 article on Climate, in the ' Encyclopedia Britannica.' Four 

 thermometers constructed for the purpose with long stems were 

 sunk beside each other at the depths of 1, 2, 4, and 8 feet,- in a 

 soft gravelly soil, which turned at 4 feet below the surface into 

 quicksand, or a bed of sand and water. It Avas found that during 



