Emission and Transmission of Heal 43 



excesses of temperature between 20 F. and 350 F., the first in 

 the ratio of i to 2.2, the second in the ratio i to 2. Newton's 

 Law is approximately true for small excesses of temperature 

 only. 



806. To sum up we have 



M=R + A = i2$.>]2Kae (y + 0.552 A"/ 1 ' 233 * 

 But we can always in practice calculate the valves of R and 

 A by Newton's L,aw corrected by the coefficients of figures i, 2 

 and 3, thus obtaining by simple calculations results that are quite 

 sufficiently accurate. 



807. We will apply this method to a case which frequently 

 presents itself; that of a horizontal cast iron pipe containing 

 steam at 212 F. and with a surrounding temperature of 59. 

 Forr=2" ;=i53X .688 X 1.52 X i + 153 X .58 X 1.56 = 298 



= 4 "M= " " " + " X-50X "=279- 



= 6" M= " " " + " X-47X "=261 



The results are in B. T. U. per square foot of surface per hour. 

 The weights of steam condensed by direct experiment are a little 

 greater, probably on account of water mechanically entrained by 

 the steam. 



809. For a horizontal pipe of sheet iron 10 inches in dia- 

 meter containing air at 302 F., the exterior air being at 59, we 

 would have M = 243 X .567 X I.88X i + 243 X .48 X 1.73=462 

 B. T. U. per hour per square foot.f 



Emission of Heat from Pipes to Air. 



821. ^mission of heat from the surface of a pipe to the air 

 traversing the pipe. The surface being maintained at a constant 

 temperature. 



Let us consider a metal pipe, the surface of which is main- 



* In French units. 



t It will be noticed that in these examples the second coefficient by which K is multi- 

 plied in order to obtain R is unity. This is because the temperature of the surrounding: 

 objects is 59 F. See figure 3, page 21. 



To sum up we have for our working formula, 



In which, 



M= B. T. U. per square foot per hour. 



R= " " due radiation. 



A " " due air contact. 



T = temperature of the body emitting heat in F . 



