364 Mr. S. P. Owen on Radiation 



Putting tf 2 + a 2 + & 2 = y, 



the first part =s4 1 — , ._^L— dy 



=4 [v/y 2 ~4a 2 6 2 ]. 



.-. Total Integral = ~ [s/fa* + a* +■&)*-- 4a?V 



- y/W+tf + Vy-taW - a-! 2 + ar a 9 ]. 

 When the wall and disk are " full " radiators then 



N= R = cr . (T/-T/), 



IT TT 



where R is the total radiation, a the Badiation Constant, 

 T l and T 2 the absolute temperatures of the cylinder and disk 

 respectively. 



.*. Amount of heat received by the disk 



= ^ (T 1 4 -lV)[ v /(^ + « 2 + /> 2 ) 2 -4^ 



§ 2. Experimental Verification . 



Using the above result, the radiation constant o- was 

 determined by the following experiment : 



The apparatus consisted of an ordinary steam jacket, the 

 inside of which was covered by an even layer of lampblack 

 obtained by the burning of camphor. This was fixed in a 

 vertical position. 



The amount of heat radiated to a copper plate .was 

 measured by means of a modification of Bunsen's Ice 

 Calorimeter. The plate consisted of the bottom of a copper 

 calorimeter, enclosed in a block of wax, the bottom being 

 exposed, sheer with the surface of the wax. A capillary 

 tube, previously calibrated, was fitted through a rubber 

 stopper to the top of the calorimeter. The inside of the 

 vessel was filled with crushed ice and water, and by fitting 

 in the stopper the capillary tube could easily be filled with 

 the water from the vessel. By observing the rate at which 

 the meniscus in the capillary moved, the amount of contrac- 

 tion and hence the amount of heat given up to the ice in 

 unit time could be calculated. 



