204 ESSAY 



but the loss, which it hence suffers, is more or 

 less compensated by what is radiated to it, from 

 the body above, the under-surface of which 

 possesses always the same, or very nearly the 

 same temperature as the air. In this way there- 

 fore, is to be accounted for the warmth of the 

 substances, which were sheltered from the sky 

 by the raised board, the pasteboard roof, and 

 the hollow cylinders of earth and pasteboard. 

 In these examples, the interposed substances 

 cannot be supposed to have remitted more heat 

 than they received. But in situations where 

 large masses of bare solid matter exist, which 

 are warmer than the atmosphere, from the heat 

 of the preceding day or other causes, a greater 

 heat will be received by the exposed body, than 

 what is radiated by itself. For example, it 

 seems certain to me, that the houses, surround- 

 ing LincolnVInn Fields, had an influence upon 

 my thermometers, during my experiments there 

 at night, beyond what arose from their merely 

 returning a quantity of heat, equivalent to that, 

 which they received from the surface of the 

 garden. It is not, however, absolutely requi- 

 site, that a body should be itself exposed to the 

 sky on a clear and calm night, in order to be- 

 come colder than the atmosphere ; exposure to 

 the influence of another body, so situated, is 

 sufficient for the production of a slight degree 



