252 



Tables 286, 287. 

 COOLING BY RADIATION AND CONVECTION. 



TABLE 286. — At Ordinary Pressures. 



According to McFarlane* the rate of loss of heat by a sphere 

 placed in the centre of a spherical enclosure which has a 

 blackened surface, and is kept at a constant temperature of 

 about 14° C, can be expressed by the equations 



e — .000238 + 3.06 X 10-0/ — 2.6 X io-«^, 



when the surface of the sphere is blackened, or 



e — .000168 + 1.98 X 10-6/ — 1.7 X io-a/«, 



when the surface is that of polished copper. In these equa- 

 tions, e is the amount of heat lost in c. g. s. units, that is, 

 the quantity of heat, small calories, radiated per second per 

 square centimeter of surface of the sphere, per degree differ- 

 ence of temperature t, and t is the difference of temperature 

 between the sphere and the enclosure. The medium through 

 which the heat passed was moist air. The following table 

 gives the results. 



TABLE 287. — At Different Pressures. 



Experiments made by J. P. Nicol in Tait's Labo- 

 ratory show the effect of pressure of the en- 

 closed air on the rate of loss of heat. In this 

 case the air was dry and the enclosure kept at 

 about 8° C. 



Smithsonian Tables. 



* " Proc. Roy. Soc." 1872. 

 t " Eroc. Roy. Soc." Edinb. 1869. 

 See also Compan, Annd. de chi. et phys. 26, p. 526. 



