168 ESSAY 



similarly situated, the greatest excess of cold 

 ever observed by me, in the larger metallic 

 plates, from this cause, over that of the air, 

 being not more than 3 or 4 degrees. If much 

 smaller pieces were placed upon grass, the re- 

 sult was different. For I have found a small 

 thermometer placed in this situation, while in- 

 closed in a sheath of gilt paper, to be only 3 

 less cold than the surrounding grass, during a 

 night favourable to the production of cold on 

 the surface of the earth. 



I collected only a few facts respecting the 

 comparative temperatures of different metals, 

 when they were exposed together to the sky, 

 on dewy nights ; but such as I did collect tend 

 to prove, that the most readily dewed metals 

 become colder than the air, sooner than those, 

 which receive dew with greater difficulty. 



Many of the experiments, which have been 

 mentioned in this section, shew, that when bo- 

 dies, which had been equally exposed to the 

 night air, were examined at the same time, 

 those which were most dewed were also the 

 coldest. No such correspondence, however, 

 was found in the experiments of different 

 nights, or even of different parts of the same 

 night. Thus, during two nights, on which 



