ON DEW, &c. 253 



disposition of things, therefore, nothing existed 

 to prevent the free passage of air from the ex- 

 posed grass, to that which was sheltered, except 

 the 4 small sticks, and there was no substance 

 to radiate heat downwards to the latter grass, 

 except the cambric handkerchief. The tem- 

 perature of the grass, which was thus shielded 

 from the sky, was upon many nights afterwards 

 examined by me, and was always found higher 

 than that of neighbouring grass which was un- 

 covered, if this was colder than the air. When 

 the difference in temperature, between the air 

 several feet above ihe ground and the un- 

 sheltered grass, did not exceed 5, the sheltered 

 grass was about as warm as the air. If that 

 difference, however, exceeded 5, the air was 

 found to be somewhat warmer than the shel- 

 tered grass. Thus, upon one night, when fully 

 exposed grass was 11 colder than the air, the 

 latter was 3 warmer than the sheltered grass j 

 and the same difference existed on another 

 night, when the air was 14 warmer than the 

 exposed grass. One reason for this difference, 

 no doubt, was that the air, which passed from 

 the exposed grass, by which it had been very 

 much cooled, to that under the handkerchief, 

 had deprived the latter of part of its heatj an- 

 other, that the handkerchief, from being made 

 colder than the atmosphere by the radiation of 



