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 near the freezing point, provided the surface is covered 

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

 while the soil beneath remained at Sl"^ ; and although a severe frost followed this rcduc, 

 lion, yet many vegetables were preserved from destruction by the caloric which the earth 

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

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

 Delaware river, when the vegetation was just putting forth. On tliis mountain, the shrubs 

 which had already leaved, or had partially leaved out, and some which had blossomed, 

 were not in the least aflected by the frost. 



The accumulation of heat often preserves the roots of corn, and other crops, when the 

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

 maize, planted however 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 60° in order to excite germination, whicli, if once secured, the grain 

 seems to be safe, though it may not ajipear above ground for some time. 



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

 more heat than tlie slopes at their 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 54° fell when the earth was 49°, and 

 the surface was raised soon after to 51°. 



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

 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 3'ear. The water of a large cistern, whose surface is four feet beneath the sur- 

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

 the whole period of excessive 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 materially from that usually followed in tlie analysis of a mineral. One hun-r 

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

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

 upon a clean mental pl.ite. The loss is 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 



