258 ESSAY 



trees and tall shrubs, which rise above the snow, 

 are little affected by cold from this cause. For 

 their outermost twigs, now that they are de- 

 stitute of leaves, are much smaller than the 

 thermometers suspended by me in the air, which 

 in this situation very seldom became more than 

 Q colder than the atmosphere. The larger 

 branches too, which, if fully exposed to the sky, 

 would become colder than the extreme parts, 

 are, in a great degree, sheltered by them ; and, 

 in the last place, the trunks are sheltered both 

 by the smaller and the larger parts, not to men- 

 tion that the trunks must derive heat, by con- 

 duction through the roots, from the earth kept 

 warm by the snow *. 



In a similar way is partly to be explained the 

 manner, in which a layer of earth or straw pre- 

 serves vegetable matters in our own fields, from 

 the injurious effects of cold in winter. 



V. The bare mention of the subject of this 

 article will be apt to excite ridicule, it being an 

 attempt to show, in what way the exposure of 

 animal substances to the moon ? s light promotes 

 their putrefaction. I have no certain knowledge, 



* It may be remarked here, however, that a thick covering 

 of snow, while it renders the surface of the earth warmer 

 that it would otherwise be, must occasion the lower atmo- 

 sphere to be colder, by preventing the passage of the heat of 

 the ground to the air, either by radiation or conduction. 



