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XXXII. On Radiation from a Cylindrical Wall. 

 By S. P. Owen, B.Se. Wales*. 



IN the experiments conducted by Todd (Proc. Roy. Soc. A. 

 vol. lxxxiii. (1909)) on the thermal conductivity of gases, 

 the problem of the effect of the radiation from the cylindrical 

 vertical wall on to the horizontal lower disk arose. The effect 

 was not calculated but was eliminated by experimental means 

 (I.e. p. 20). 



In the following paper an expression is deduced for the 

 amount of lieat radiated from a cylindrical vertical wall 

 similar to the insulating ring in Todd's experiments, to a 

 horizontal circular plate placed near the bottom. 



The conditions are slightly different from those obtaining 

 in Todd's experiments, in that here the temperature of the 

 wall is assumed constant whereas in the insulating ring there 

 is a linear gradient of temperature from the top to the 

 bottom. Very little alteration is needed in the calculation 

 to fit these latter conditions. 



The result is tested by obtaining values of the Radiation 

 Constant by a simple experiment which makes no claim to 

 great accuracy. The values obtained agree closely with the 

 accepted value. The experiment is described in the second 

 part of the paper. 



§ 1. Theoretical. 



Let a = radius of cylinder, 



b = AO = radius of the copper plate. 



Consider two elements of surface, one at G and the other 

 on the plate at F. 



Let be the angle between two vertical planes, one con- 

 taining GN the diameter of the cylinder through G and the 

 other GH, a line in the same horizontal plane as GN, the plane 

 cutting the plane of the plate in the line DF. 



Since the plate is symmetrically placed with respect to the 

 cylinder, evidently EI)C=:0. 



GF is the line joining the two elements at G and F making 

 angle <j> with GH. 



Taking D as the origin let DF = ?< and DG = .i'. 



* Communicated bv Prof, G. W. Todd, D.Sc, 



