THE NEW SCIENCE OF METEOROLOGY 



the closed shutter shielded the glass which it covered 

 from the heat that was radiated to the windows by 

 the walls and furniture of the room, and thus kept it 

 nearer to the temperature of the external air than 

 those parts could be which, from being uncovered, re- 

 ceived the heat emitted to them by the bodies just 

 mentioned. 



" In making these experiments, I seldom observed 

 the inside of any pane to be more than a little damped, 

 though it might be from eight to twelve degrees colder 

 than the general mass of the air in the room ; while, in 

 the open air, I had often found a great dew to form on 

 substances only three or four degrees colder than the 

 atmosphere. This at first surprised me ; but the cause 

 now seems plain. The air of the chamber had once 

 been a portion of the external atmosphere, and had 

 afterwards been heated, when it could receive little ac- 

 cessories to its original moisture. It constantly re- 

 quired being cooled considerably before it was even 

 brought back to its former nearness to repletion with 

 water ; whereas the whole external air is commonly, at 

 night, nearly replete with moisture, and therefore 

 readily precipitates dew on bodies only a little colder 

 than itself. 



' When the air of a room is warmer than the external 

 atmosphere, the effect of an outside shutter on the 

 temperature of the glass of the window will be directly 

 opposite to what has just been stated; since it must 

 prevent the radiation, into the atmosphere, of the heat 

 of the chamber transmitted through the glass. 



11 2. Count Rumford appears to have rightly con- 

 jectured that the inhabitants of certain hot countries, 



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