180 The Aether as an Elastic Solid. 



where 



a /p\l . b 



- = - - COS I, 



c \n c 



/p\* 



- - I sin ^ ; 

 \nj 



here * denotes the angle of incidence, p the inertia of the aether,, 

 and n its rigidity. 



Let the reflected light be a function of the argument 



OiX + by + ct, 



where, in order to secure continuity at the boundary, b and c 

 must have the same values as before. Since Green's formulae 

 are to be still applicable, we must have 



where sin i = ft sin r, but /j. has now a complex value. This- 

 equation may be written in the form 



n 

 Let the complex value of /u, z be written 



p 



the real part being written pi/p in order to exhibit the analogy 

 with Green's theory of transparent media : then we have 



n n 



But an equation of this kind must (as in Green's theory) 

 represent the condition to be satisfied in order that the 

 quantity 



(a\x + by + ct) \/ - I 

 t/ 



may satisfy the differential equation of motion of the aether ; 

 from which we see that the equation of motion of the aether 

 in the metallic medium is probably of the form 



d z e z A de z 



This equation of motion differs from that of a Greenian 



