410 Action of the Atmosphere upon neiohj-deepened Soil. 



beinjT 65"^, ascertained that the temperature of the upper two 

 inches of s^ard en- mould exposed to the sun's rays was 84°, at four 

 inclies deep G9°, But the thermometer in the shade, as I shall 

 afterwards show, has been noticed in England as high as 96° F. ; 

 the soil therefore must occasionally attain a heat almost approach- 

 ing to that observed by Herschel. 



This heat will be affected to a considerable degree by the con- 

 dition of the soil as to dryness, the evaporation of any moisture 

 it may contain reducing the temperature considerably ; this de- 

 pression, according to Schubler, amounts to 11^° or 13^° F. 

 Schubler made some of the most careful investigations we pos- 

 sess as to the warming of soils by the sun. With surfaces of 

 the same colour he found that the materials composing the soil 

 made little difference in its capacity to become heated, provided 

 they were in similar states as to dryness ; sand, clay, loam, gar- 

 den-mould, &c., showing very little dffference with the thermo- 

 meter. Colour, however, had a powerful effect; for the com- 

 munication of a dark tint he employed lamp-black, and for 

 white fine magnesia, sprinkling these over the surface by means 

 of a fine lawn sieve. Although exposed to the sun for hours, the 

 differently coloured earths never attained the same temperature, 

 the lighter coloured always remaining considerably cooler. The 

 folio win": are some of his results : — 



Ivinds of Earth exposed to the Sun's rays between U 



and 3 o'clock in the latter part of August : temperature 



in the shade 724° to 77° Fahr. 



Siliceous sand — bright yellowish grey 

 Calcareous sand — whitish grey 



Sandy clay— yellowish 



Loamy clay — yellowish 



Stiff clay — yellowish grey 



Fine bluish-grey clay 



Garden mould — blackish grey . . 



Arable soil — grey 



Slaty marl — brownish red 



Mean of the highest Temperature of 



the surface uf the Earths iu the 



shade, 77° Fahr. 



Surface of 

 Natural Colour. 



Wet. 



99-1 

 99-3 

 98*2 

 99-1 

 99'3 



99 -r) 



99-5 



97-7 

 101-8 



Dry. 



112-6 

 112-1 

 111-4 

 112 1 

 112-3 

 113-0 

 113-5 

 111-7 

 115-3 



With Dry Earth. 



With a 

 White 

 Surface. 



109-9 

 109-9 

 108-3 

 107-8 

 107*4 

 106-3 

 108-3 

 107-C 

 108-3 



With a 

 Black 



Surface. 



123-6 



124-0" 



121-6 



121-1 



120-4 



1-20-0 



122-5 



1220 



123-4 



The earths were placed in vessels with four square inches of 

 surface and half an inch deep, thermometers being placed in them 

 so as to have their bulbs covered one-eighth of an inch high with 

 earth. 



Sir H. Davy says, " I found tliat a rich black mould, which 

 contained one-fourth of vegetable matter, had its temperature 



