L I** 3 



When soils are perfectly dry, those that most 

 readily beceme heated by the solar rays likewise cool 

 most rapidly; but I have ascertained by experiment, that 

 the darkest coloured dry soil (that which contains 

 abundance of animal or vegetable matter; substances 

 which most facilitate the diminution of temperature,) 

 when heated to the same degree, provided it be with- 

 in the common limits of the effect of solar heat, will 

 cool more slowly than a wet pale soil, entirely com- 

 posed of earthy matter. 



I found that a rich black mould, which contained 

 nearly i of vegetable matter, had its temperature in- 

 creased in an hour from 65 to 88 by exposure to 

 sunshine; whilst a chalk soil was heated only to 69 

 under the same circumstances. But the mould re- 

 moved into the shade, where the temperature was 62 $ 

 lost, in half an hour, 15; whereas the chalk, under 

 the same circumstances, had lost only 4. 



A brown fertile soil, and a cold barren clay were 

 each artificially heated to 88% having been previously 

 dried: they were then exposed to a temperature of 57; 

 in half an hour the dark soil was found to have lost 9 

 of heat; the clay had lost only 6. An equal portion 

 of the clay containing moisture, after being heated to 

 88, was exposed in a temperature of 55; in less than 

 a quarter of an hour it was found to have gained the 

 temperature of the room. The soils in all these ex- 

 periments were placed in small tin plate trays two 

 inches square, and half an inch in depth; and the tem- 

 perature ascertained by a delicate thermometer. 



Nothing can be more evident, than that the 



