Applications of the Formulas 97 



Consider for example, a room with but one wall exposed to 

 the outer air, with 4.305 square feet of glazed windows and 64.6 

 square feet of walls of 19.7 inches thich ; the interior temperature 

 being 59 and the outer temperature 42.8 the total quantity of 

 heat transmitted will be ; (S68 and 88 ij. 



43.05X8.5 + 64.6X5-05 = 366 + 326 = 692. 



If we suppose the exterior temperature to fall to 32 , the 

 quantity of heat transmitted by the windows will rise immediately 

 from 366 to 6 1 1 , whilst the transmission of heat through the walls 

 will rise very slowly in 32 hours, * from 326 to 546, and as a 

 matter of fact the rise will be much slower. Thus the windows 

 have a much greater influence than the walls on the variation of 

 the interior temperature or on the quantity of heat which must 

 be supplied to maintain this temperature, at least unless the walls 

 are very thin and their area very large relative to that of the win- 

 dows. 



906. As it is important to have a clear idea of the variations 

 of temperature which take place at the surfaces of walls during 

 the heating season, as well as the quantities of heat transmitted 

 and the quantities of heat contained in the walls, I have computed 

 these different elements for walls of 19.70, 39.37 and 59.07 inches 

 in thickness according to the formulas (870) which assume all 

 the walls exposed to the outer air. I have taken C=i3.jilF= 

 .737 and A^ = .4o whence 15=1.137; and have assumed the 

 specific gravity of the stone to be 2.2 and its specific heat to be .2. 

 Then the quantity of heat contained per square foot of wall at 

 the temperature v will be 



i X X62.4X 2.2X2 z>=2.288 e v 

 12 



When the temperatures vary uniformily from /to /', between the 

 two surfaces, the quantity of heat contained in the wall, reckoned 



from O would be /+ /' we will designate this quantity 



2.288^ ; 

 2 



by A and we will have, calling the interior temperature of the 

 room T and the exterior temperature : 

 for ^=19.7 inches. 



*See foot-notes to 904 



