CHAPTER IX 



RELATION OF SPECIFIC INDUCTIVE CAPACITY 

 TO REFRACTIVE INDEX. THE MEASURE- 

 MENT OF SPECIFIC INDUCTIVE CAPACITY 



The relation between specific inductive capacity and n-fr iciiv.- index in 

 the electro-magnetic theory of light Determinations of specific induc- 

 tive capacity Boltzmann'e condenser method for solids His exp- 

 ments with crystalline sulphur Hopkinson's exprriim-tit^ Boltzmann's 

 experiments on gases Specific inductive capacity of water, alcohol, ami 

 other electrolytes Experiments of Colin nnd Arons,Rosa, Hcerwa^r 

 and Nernst Experiments of Dewar and Fleming at low temperatures 

 Drude's experiments with electric waves. 



The relation between specific inductive capacity and 

 refractive index in the electro -magnetic theory of light. 



Maxwell's electro-magnetic theory of light MippoM> that light 

 consists of waves of electric strain transverse to the direction of 

 propagation accompanied hy magnetic induction perpendicular to 

 the electric strain, and also transverse to the direction of propaga- 

 tion. If, for instance, the light is plane polarised, we mu-t -nppose 

 the electric strain always in one plane, say that of the paper as 

 represented by the vertical lines in Fig. 82, and alternately up and 

 down in successive half wave-lengths. The accompanying magu 



Fio. 82. 



induction will be in a plane perpendicular to that of the paper, and 

 alternately in and out in successive half wave-lengths. An analogy 

 with sound waves will suggest to us the ratio of the veloci ties of pro- 

 pagation in different media. The full investigation belong to 

 Optics. 



In sound waves there are the two types of energy, elastic strain 

 and kinetic, and the velocity of propagation is given 1>\ 



y _ /modulus of bulk elasticity 

 density 



The numerator is proportional to the energy stored per unit 



120 



