ESSAY 



\ 



which it forms, superior to that of the neigh- 

 bouring atmosphere. My observations, how- 

 ever, on the temperature of metals, when ex- 

 posed to the sky on dewy nights, were less 

 numerous, than those on several other subjects 

 treated in this Essay, by reason of the less fre- 

 quent opportunity I enjoyed of making them ; 

 and many of those, which I did make, were 

 afterwards found by me to have been impro- 

 perly conducted. I thought, for instance, for 

 some time, that the temperature of a metal, on 

 a dewy night, might easily be learned in the 

 way, in which I had been accustomed to ascer- 

 tain the temperature of dewed grass. But, ob- 

 serving dew one night on the glass tube of a 

 thermometer, which was lying on a metal placed 

 upon grass, while the metal itself was free from 

 moisture, I conceived it probable, that the cold 

 then indicated by the thermometer was not the 

 real temperature of the body, to which it was 

 applied. To determine the point, I placed on 

 the same metal a second thermometer, covered 

 with gilt paper, upon which this was found at 

 three observations to be 6J, 7, and 7 higher 

 than the other. In this experiment, the bulb 

 of the naked thermometer, from being very 

 small, did not project as far as the outer surface 

 of the scale, and, consequently, did not come 



