ON DEW, &c. 



173 



generally about lower, than another in the 

 air. That this difference was not owing to 

 evaporation was proved by the thermometer on 

 the snow always rising, from a half to a whole 

 degree, whenever the air was a little moved, 

 and falling the same quantity, as soon as a great 

 stillness again took place. 



I had no opportunity of renewing my observa- 

 tions upon snow, before the beginning of the 

 present year, 1814. The state of my health 

 rendering it improper, that I should incur 

 much fatigue, or be long exposed to night air, 

 I restricted myself to the making a few experi- 

 ments, in the large garden in Lincoln's-Inn 

 Fields. I went thither, for the first time, on 

 the evening of the 4th of January, immediately 

 after a considerable snowfall had ceased, wish- 

 ing to begin my observations, before any cold 

 should arise on the snow's surface, from ex- 

 posure to the sky. This was desirable on an- 

 other account ; for Mr. Kirwan, in direct op- 

 position to indisputable facts, most clearly stated 

 by Mr. Wilson, had said, that the great cold, 

 observed by that gentleman on snow, was occa- 

 sioned by this substance having retained the 

 temperature of the high region, from which it 

 had fallen*. The result of my inquiry was, 

 that the surface of the snow, and the air 4 feet 

 * On Temperatures, p. 30. 



