Emission and Transmission of Heat 41 



This loss of heat per square meter per hour is given by the 



formula, 



,4=0.552 A"/ 1 ' 233 ...... (3) 



where / represents ( in Centigrade degrees) the constant excess of* 

 the temperature of the body, over that of the surrounding air, 

 and K' a number which varies with the form and dimensions of 

 the bodies.* 



798. For spherical bodies we have, in English units, 



, 1.048 

 K = .363 H -- 



where r= radius in inches. 



799. For horizontal cylinders of circular section we have, 

 in English units, 



where r equals the radius in inches, f 



800. In the case of vertical cylinders, the cooling depends 

 both on their height and diameter, and 



here r = radius in inches and h = height in feet.J 



802. For vertical plane surfaces, the value of A" is given 

 by the formula 



where h is the vertical height of the surface in feet. 



804. Figure i, page 21, gives the coefficients by which 

 the value of A" obtained by the formulas above, must be multi- 

 plied in order to correct for the differences in temperature between 

 the body and the surrounding air. 



805 . It is apparent from an inspection of Figures i , 2 and 

 3 that Newton's Law is extremely inaccurate; the coefficients or 

 the values of R and A, instead of remaining constant vary fof 



*It is important to note that by the temperature of the surrounding air is meant its 

 temperature before it is in any way influenced by the heat emitted from the cooling body 



t Figure 4, page 24 gives the values of K' for the horizontal cylinders up to 16 inches, 

 diameter. 



t Figure 5, page 25, gives the values of A"' for cylinders up to 18 inches diameter. 



\ See Figure n. 



