EELATIONS OF THE SOIL TO HEAT. 191 



Schiibter made observations ou the temperatures at- 

 tained by various dry soils exposed to the sun's raySj 

 according as their surfaces were blackened by a thin 

 sprinkling of latnp-black or whitened by magnesia. Ilis 

 results are given in columns 1 and 2 of the following table 

 {ride p. 196,) from which it is seen that the dark surf\ce 

 was warmed 13° to 14° more than the white. We like- 

 wise notice that the character of the very surface deter- 

 mines the degree of warmth, for, under a sprinkling of 

 lamp-black or magnesia, all the soils experimented with 

 became as good as identical in their absorbing power for 

 the sun's hent. 



The observations of Mnlaguti and Durocher prove that 

 the peculiar temperature of the soil is not always so 

 closely I'elated to color as to other qualities. They studied 

 the thermometric characters of the following soils, viz. : 

 Gai-den earth of dark gray color, — a mixture of sand and 

 gravel with about five per cent of humus ; a grayish- 

 white quartz sand ; a grayish-brown granite sand ; a fine 

 light-gray clay (pipe clay) ; a yellow sandy clay ; and, 

 finally, four lime soils of different physical qualities. 



It was found that Avhen the exposure was alike, the 

 dark-gray granite sand became the warmest, and next to 

 this th'' grayish-white quartz sand. The latter, notwith- 

 standing its lighter color, often acquired a higher temper- 

 ature at a depth of four inches than the former, a fact to 

 be ascribed to its better conducting poAver. The black 

 soils never became so warm as the two just mentioned. 

 After the black soils, the others came in the following oi-- 

 der : garden soil ; yellow sandy clay ; pipe clay ; lime 

 soils having crystalline grains ; and, lastly, a pulverulent 

 chalk soil. 



To show what different degrees of warmth soils may 

 acquire, under the same circumstances, the following max- 

 imum temperatures may be adduced : At noon of a July 

 day, when the temperature of the air Mas 90°, a thermoni' 



