234 COMPOSITION 



ripening of fruits and fall crops. There is sufficient caloric retained to preserve the tempe- 

 rature of the surface when the air is aear the freezing point, proi ided the surface is covered 

 ami its radiation checked. On one occasion, the temperature of the air was reduced to 26°, 

 while the Boil beneath remained at 51 ; and although a severe frost followed iliis reduc- 

 tion) yet main vegetables were preserved f i destruction by the caloric which the earth 



had accumulated the preceding week, and which was then given off. This instance of the 

 accumulation of heat in the soil occurred upon one of t lie high peaks at the head of the 

 Delaware river, when the vegetation was jum putting forth. On this mountain, the Bhrubs 



which had already leaved, or had partially leaved OUt, and some which had hlossonied, 



were not in ihe least affected by the frost. 



The accumulation of heat Often preserves t lie roots of coin, and other crops, when the 

 herbage is destroyed. When the temperature of the surface is 60°, we have found that 

 maize, planted how e\ er early, comes up ; while if planted when the temperature is several 

 degrees lower, although later in the season, it will certainly rot. The temperature must 

 reach the point of GO in order to excite germination, which, if once secured, the grain 

 seems to be Bafe, though it may not appear above ground for some time. 



From a few observations which we have made, it appears that mountain soils absorb' 

 more heat than the slopes ai I heir base. 



The surface heat is often preserved in autumn by rain. In the spring, too, rains aid in 

 warming the earth. A rain whose temperature was ~A fell when the earth was 49 a , and 



the surface was raised soon alter to 51°. 



The highest temperature of the ground, which has been observed, was 72°. This tem- 

 perature has been maintained with little variation for several successive days, in August, 

 the present year. 1846. The earth acquired nearly the same temperature about the same 

 period last year. The water of a large cistern, whose surface is four feet beneath the sur- 

 face of the ground, acquired the temperature of the earth, which it has maintained during 

 the whole period of excessiw heat 



VII. COMPOSITION OF THE SOILS OF NEW-YORK. 



Several methods have been proposed for the analysis of soils, each of which has its par- 

 ticular advantages. The method which has been followed in the New-York Survey has 

 not differed tnateriallj from thai usually followed in the analysis of a mineral. One hun- 

 dred grains of the sifted soil is taken titter it is dried in its envelope, and exposed to a 

 temperature of about 300°, on a piece of glazed paper, or until the paper is slightly browned, 

 upon a clean metal plate. Tie- Loss i- set down as water. It is then exposed to a red heat, 

 and stirred in a platina capsule, until its blackness has disappeared : thus its organic 



