﻿47(3 Prof. D. X. Mallik on the 



Now, assuming the solutions 



weget »*=l+S- 



p 2 —ipb ~p 1c - 



showing that there is absorption in this case. 



If /> is very nearly equal to p, b cannot be neglected ; 

 this further indicates that there is always absorption, under 

 these circumstances. 



If p is very small., then n 2 =n 2 + — _ 5__r- and the real 

 part of n is ?° ~ l P b ° 



( 1 1 4 , 2 , 2 1 where a — zn 2 c. 



As y> increases ;i diminishes. This explains anomalous dis- 

 persion. 



20. It is not without interest to compare the above with 

 the various elastic solid theories that have been proposed for 

 the explanation of dispersion. 



27. For this, let us recall the fact that in an elastic 

 medium there is, associated with an elastic displacement, 

 molecular rotation ; and if the properties of the medium are 

 to be capable of being expressed in terms of quantities that 

 enter into the statement of either theory, electric displace- 

 ment and magnetic force must correspond in some way with 

 the velocity of vibration and molecular rotation. Now in 

 the electrical theory we have two quantities defining the 

 property of the medium /jl and k, as well as the quantities 

 /, y, h (polarization) and H (magnetic force), while in the 

 theory of elasticity we have the constants p (density), n 

 (rigidity), and the quantities co (molecular rotation) and 

 f r) f (displacement), and it will be necessary to decide upon 

 a suitable mode of identifying these, severally. 



2$. Now, on examining the expression for energy (kinetic 

 and potential) in terms of these two sets of quantities, it is 

 easy to see that one such mode of establishing a concordance 

 between the two sets of phenomena is (as Larmor has done) 

 to identify electric displacement with molecular rotation 

 and magnetic force with ^ethereal velocity (in vibratory 

 motion). 



