248 ESSAY 



warmer than that without. Similar experiments 

 were made on many other mornings, the results 

 of which were ; that, when the warmth of the 

 internal air exceeded that of the external, from 

 8 to 1 8, the temperature of the covered panes 

 would be from 1 to 5 less than that of the 

 uncovered ; that the covered were sometimes 

 dewed, while the uncovered were dry ; that at 

 other times both were free from moisture ; that 

 the outsides of the covered and uncovered panes 

 had similar differences with respect to heat, 

 though not so great as those of the inner sur- 

 faces ; and that no variation in the quantity of 

 these differences was occasioned by the wea- 

 ther's being cloudy or fair, provided the heat 

 of the internal air exceeded that of the ex- 

 ternal equally in both of those states of the 

 atmosphere. 



The remote reason of these differences did 

 not immediately present itself. I soon, how- 

 ever, saw, that the closed shutter shielded the 

 glass, which it covered, from the heat, that was 

 radiated to the windows by the walls and furni- 

 ture of the room, and thus kept it nearer to the 

 temperature of the external air, than those parts 

 could be, which, from being uncovered, received 

 the heat emitted to them by the bodies just 

 mentioned. 



In making these experiments, I seldom 



