Tlie Rev. J. H. Jellett on the Equilibrium and Motion of an Elastic Solid. 199 



single function. This function, in the system of Professor Mac Cdllagh, is in 

 its simplest form given by the equation 



\dy dz)^ \dz dx)^''\dx~d^ 

 The function used by Mr. Green is given by the equation 



( \dz ^ dx) * dx dz 



( \dij dx) dx dy) 



Comparing these successively with the general form (T), p. 198, we see 

 that the function used by Professor Mac Cullagh cannot by any supposition 

 be identified with (T), inasmuch as it contains the products 



d^<hi d^ d£ djd^ 

 dy dz ' dz dx' dx dy ' 

 without the corresponding products 



^ dri d^ d£ dri d^ 



dz dy' dx dz' dy dx' 



To identify the function used by Mr. Green with (T), we should have, as is 

 easily seen. 



These conditions would render the body uncrystalline, and therefore incapable 

 of being generally identical with the luminous ether. 



Hence we infer, that if the supposed luminous ether be a medium such as 

 either of these writers assume it to be, the mutual action of its particles cannot 

 be independent. In other words, we must suppose that in such a medium the 

 capacity which each particle possesses of exerting force on any other particle, 

 is modified by the action of the surrounding particles. 



