24 Mr. G. W. Walker. [May 2, 



equality at times of great sun-spot frequency may be some form of 

 radiation which reduces the resistance of the atmosphere to currents 

 generated by the sun. This would explain the phenomena without 

 requiring the enormous variations in the sun's output of energy from 

 year to year that would appear necessary to account for the great 

 variations in the magnetic phenomena, variations moreover which as 

 the paper shows do not appear to be accompanied by any but the 

 most insignificant changes in the amplitude of the temperature 

 inequality at the earth's surface. The importance is pointed out of 

 reliable information as to whether atmospheric electricity potential, 

 at low and at high levels, resembles magnetic phenomena in being 

 largely different in years of large and small sun-spot frequency. 



" On the Theory of Befraction in Gases." By GEORGE W. WALKER, 

 M.A., A.E.C.SC., Fellow of Trinity College, Cambridge. Com- 

 municated by Professor J. J. THOMSON, F.R.S. Received 

 May 2, Bead May 28, 1903. 



(Abstract.) 



The present theories of refraction in gases lead to expressions for 

 the refractive index, of which the formula 



may be taken as typical. 



In the formula /* is the refractive index, N is the number of molecules 

 per unit volume, p is the frequency of the waves, and f(p) is a 

 function of p which depends on the assumptions made as to the con- 

 stitution of the molecule. 



The formula, although it explains the main features in the visible 

 spectrum, cannot always be made to explain the measured temperature 

 effects, even when allowance is made for the deviations from the 

 gaseous laws of Boyle and Charles. 



Mfttm***."*** thC diel6Ctric C nstant for some S* 868 8Uch 8 

 8Q, and NH 3 , the value of K- 1 is much greater than the value of 



- 1. In such cases we find that ^-1 varies nearly as N, while 

 7 pr P rti nal to N /*' where * the absolute 



The theories are thus inadequate, and a modification is required 

 which will gnre a greater dependence on temperature 



SSSS^j^^^s- 



periods of v.brat.on, which are naturally identified with the 



