of Maxwell's Electrical Theory. 



183 



12. For the aether at present under consideration we see by 

 equation (22) that a 2 and therefore tol is a function of the 

 time only. But it is a function (in the case of waves) of t 

 and z, i. e. it is a constant. 



Let Y of equation (32) be zero. Suppose at any instant 

 lines are drawn from all points of the axis of z equal and 

 parallel to the values of a there. Their extremities will lie 

 on a right cylinder with z for axis, and the curve they form 

 will be a complete representation of the wave. Figures 1, 2, 

 3, 4 thus represent different types of waves that can be borne 



Fig. 1. 



Fig. 2. 



Fia-. 3. 



Fig. 4. 



> 



< 



> 



by our aether. Fig. 1 is of course a circularly polarized wave. 

 Fig 2 is a wave partly plane-polarized and partly circularly 

 polarized, i. e. elliptically polarized. Fig. 3 would probably 

 appear to us as a plane-polarized, and fig. 4 as ordinary un- 

 polarized light. 



All such waves are particular ones of MaxwelPs. Now 

 Maxwell asserts that when such waves are incident on gross 

 matter the aether exerts a pressure on that matter. But as 

 we have seen, on the present theory all ponderomotive forces 

 consist of actions and reactions between different parts of 

 gross matter and never between gross matter and aether, and 

 yet for the present case our stress is exactly the same as 

 Maxwell's. The explanation of the apparent discrepancy is 

 contained in § 75 of ' Electromag.' If we find that a certain 

 stress suffices to explain certain experimental facts, there are 

 an infinite number of other stresses that will also do so. We 



