Applications of the Formulas 8 1 



88 1. Consider first that the windows are placed in the 

 exposed wall of a room having one only of its walls exposed to 

 the outer air, the inner surfaces of the other walls will be sensibly 

 at the temperature of the interior air. As the rays of obscure 

 heat do not pass through glass, the windows will be heated on 

 one side by radiation from the inner surfaces of the walls and by 

 the contact of the warm air, and will cool on the other side from 

 analogous causes. Admitting that the heating and cooling take 

 place in the same way, for the same excesses of temperature, and 

 remarking that for the small thicknesses of window glass, the 

 quantities of heat transmitted are independent of the thickness, 

 as we have already seen (865), we will have, preserving the pre- 

 vious notation, M= (Tx) Q M= (x 0) Q; from which 



"p Q 'p 



x=- andJ/= Q 



2 2 



For heights in feet of: 



3.28 6.56 9.84 13.12 16.40 



the values of K' (802) being equal to 



.492 .453 .437 .427 .420 



and the radiation of glass being equal to .596, we find for these 

 different heights and for a difference of temperature of i Fahren- 

 heit between T and 0, the following values of M. 



.542 .524 .516 .511 .508 



The greatest of these numbers is smaller than that I formerly 

 found by direct experiment, because I used a window of smaller 

 height, and did not take all the precautions which I have since 

 recognized as necessary. 



If the inside temperature was 59 and the otside 42.8, that 

 of the glass would be 50.9, and the quantities of heat emitted in 

 B T U per hour per square foot would be, for the heights we 

 have been considering : 



8.79 8.50 8.36 8.28 8.24 



882 . Let us consider now an entirely glazed enclosure heated 

 by warm air, and let us disregard the effect produced by the floor 

 or ground. The glass will only be heated by the air, since all 

 the surfaces are at the same temperature, and their mutual radi- 

 ation would therefore have no effect. We would then have, pre- 



