256 Magnetic Dispersion in Relation to Electron Theory. 



This system, which is that adopted by Lorentz in his 

 ' Theory of Electrons ' (in which, however, Heaviside's 

 rational values are used), appears to be the best adapted to 

 the interpretation of experimental results. 



Summary. 



(1) The calculation of ultraviolet free-periods from 

 ordinary dispersion leads in general to a mean effective 

 value only. Sew formulae are obtained for benzene, m. xylene, 

 and a-monobromnaphthalene. 



(2) When a similar calculation is made from magnetic 

 rotary dispersion using the formula 



the value obtained is usually much shorter and often 

 progressive. As the latter formula contains no adjustable 

 constants, this result shows that in the case of the liquids 

 here examined Meyer's formula does not apply. 



(3) When a progressive result is obtained in (2) a close 

 approximation to the longest dispersion period in the ultra- 

 violet can usually be obtained from 



/ X 2 \ 2 



This appears to be due to a much sharper differentiation in 

 the effects of bands of decreasing wave-length in the mag- 

 netic case. 



(4) In the case of benzene, and possibly also in m. xylene, 

 the longest period is almost an exact submultiple of the 

 period of one of the infra-red bands. 



I desire to express my cordial thanks to Prof. Wilberforce, 

 who has kindly placed the necessary apparatus at my 

 disposal, for the interest he has taken in the experiments; 

 to my friend Mr. G. Calderbank, B.Sc, for much valuable 

 help in the evaluation of the numerical data ; and to 

 Mr. F. W. Pye for the care and attention bestowed on the 

 construction of the solenoid. 



The George-Holt Physics Laboratory, 

 University of Liverpool. 



