122 ANNUAL REPORT OF NEW-YORK 



VIII. Cohesiveness of the soil. — A soil is said to be heavy or 

 light, not as it weighs more or less, but as it is easy or difficult to 

 work. The state of dryness lias great influence on this quality. 

 Sand, lime and humus have very little cohesion when dry, but 

 considerable when wet. Soils in which they predominate are 

 usually easy to work. But clay has entirely different characters, 

 and upon them almost exclusively depends the tenacity of a soil. 

 Dry clay, when powdered, has hardly more consistence than 

 sand, but when thoroughly moistened, its particles adhere together 

 to a soft and plastic, but tenacious mass; and in drying away, at 

 a certain point, it becomes very hard, and requires a good deal 

 of force to penetrate it. In this condition it offers great resistance 

 to the intruments used in tillage, and when thrown up by the 

 plough, it forms lumps which require repeated harrowings to 



In another trial in March, the difference in average temperature between the southern and 

 northern exposures was nearly double this amount in favor of the former. Among the soils 

 experimented on it was found that when the exposure was alike, the dark -gray granite sand 

 became the warmest, and next to this the grayiih-white quartz sand. The latter notwith- 

 standing its lighter color, often acquired a higher temperature when at a depth of four inches 

 than the former, a fact to be ascribed to its better conducting power. The black soils never 

 became so warm as the two just mentioned, demonstrating that color does not influence the 

 absorption of heat so much as other qualities. After the black soils, the others came m the 

 following order: Garden soil, yellow sandy clay, pipe clay, lime soils having crystalline 

 grains, and lastly a pulverulent chalk soil. 



To show what diilerent degrees of warmth, soils may acquire under the same circumstances, 

 the following maximum temperatures may be adduced. At noon of a July day, when the 

 temperature of the air was 90*^, a thermometer placed at a depth of little more than one 

 inch, gave these results: 



In quartz sand, 126'* 



In crystaline lime soil, 115° 



In garden soil, • 114** 



In yellow sandy clay, 1 00* 



In pipe clay, 94® 



In chalk soil, 87° 



Here we observe a difference of nearly 40° in the temperature of the coarse quartz and the 

 chalk soil. The experimenters do not mention the influence of water in affecting these 

 results — they do not state the degree of dryness of these soils. It will be seen, however, 

 that the warmest soils are those that retain least water, and doubtless something of the 

 slowness with which the fine soils increase in warmth is connected with the fact that they 

 retain much water, which in evaporating appropriates and renders latent a large quantity 

 of heat. 



Malnguti and Durocher also studied the eff'ect of a sod on the temperature of the soil. 

 They observed that it hindered the warming of the soil, and indeed to about the fame extent 

 as a layer of earth, of three inches depth. Thus a thermometer four inches deep in green- 

 sward, acquires the same temperature as one seven inches deep in the same soil not grassed. 



It is to be remembered that the soils that warm most quickly, al<o cool correspondingly 

 fast, and thus are subjected to the most extensive ai d rapid changes of temperature. The 

 greensward which warms slowly, retains it^ warmth most tenaciously, and the sands that 

 become hottest at noon-day, are c.ldsst at midnight. 



