412 Action of the Atmosphere upon ■nevohj-deepened Soil 



which are marked as having been made in fine weather exhibit 

 the mean highest temperature of an ordinary blackish-grey gai'den 

 mould, as observed on the south side of my house between noon 

 and one o'clock, whenever the weather happened to be perfectly 

 fine at that part of the day. They are founded on the average of 

 two years' observations ; the bulb of the thermometer was covered 

 only tV of an inch high v/ith earth. Those figures in the table 

 which refer to variable weather rest on observations made, in the 

 Botanic Garden at Geneva in the year 1796 ; they contain the 

 mean of the observations made every day, and not merely of those 

 taken in fine weather." 



The above observations will serve in some degree to show to 

 what a high degree of warmth the surface-soil will attain under a 

 clear sun, even where the temperature of the air in the shade is 

 similar to what frequently occurs in this country. Under such a 

 degree of heat the decomposition of the organic matter of the soil 

 must go on at a great rate, with the evolution of much ammonia 

 and carbonic acid, agents which, as will be afterwards shown, play 

 an important part in the modifications of the mineral matter of 

 the soil. It may be also gathered from the last table what eleva- 

 tions of temperature the surface of the ground may be expected 

 to attain above that of the air in the shade, as usually recorded 

 in meteorological registers. It will be observed also that in one 

 case, at Tubingen, the soil rose 75 above that of the air, when the 

 latter was at 78" F. Bearing this in mind, and glancing over the 

 shade temperatures which will be found subjoined, the conclusion, 

 I think, cannot be avoided that in some countries the ground must 

 attain a degree of heat much above any yet recorded, perhaps 

 occasionally approaching 200° F. 



Temperature 



of Air 

 in the Shade. 



Authority. 



Near Maidstone, in Kent; 7 June, "I 



1846 / 



Clapham ; July, 1808 



? Buckinghamshire ; July, \8tio 



Esne, in Upper Egypt 



Near the Euphrates, in the Desert 



Salt Lake of Bahr Assal 



Arabia 



Nubia 



Northern Circars, India ; at -midA 

 night in 1799 / 



94- 



96- 



96* 



117* 

 132' 

 126' 

 120- 

 130- 



108- 



G. H. Fielding, Proceed, of Koyal 

 Soc, V. 625. 



Cavendish, Eeg. of Royal Soc. 

 ("Dr. Heberden, Proceed, of Koyal 

 \ Soc, ii. 260. 



Burckhardt. 



Griffiths, Travels in Arabia. 



Harris, Highlands of Ethiopia. 



Encyc. Brit., 8th ed., iii. 737. 



Thompson's Meteorology, p. 56. 



Ditto, p. 55. 



The following table shows some of the greatest degrees of 

 natural cold that have been observed in this and other countries : — 



