2 Mr GREEN, ON THE REFLEXION 



assigned portion of the mass will always be the exact differential of 

 some function. But, this function being known, we can immediately 

 apply the general method given in the Mecanique Analytique, and 

 which appears to be more especially applicable to problems that re- 

 late to the motions of systems composed of an immense number of 

 particles mutually acting upon each other. One of the advantages of 

 this method, of great importance, is, that we are necessarily led by 

 the mere process of the calculation, and with little care on our part, 

 to all the equations and conditions which are requisite and sufficient 

 for the complete solution of any problem to which it may be applied. 



The present communication is confined almost entirely to the con- 

 sideration of non-crystallized media; for which it is proved, that the 

 function due to the molecular actions, in its most general form, con- 

 tains only two arbitrary coefficients, A and B ; the values of which 

 depend of course on the unknown internal constitution of the medium 

 under consideration, and it would be easy to shew, for the most gene- 

 ral case, that any arbitrary disturbance, excited in a very small portion 

 of the medium, would in general, give rise to two spherical waves, 

 one propagated entirely by normal, the other entirely by transverse, 

 vibrations, and such that if the velocity of transmission of the former 

 wave be represented by y/A, that of the latter would be represented 

 by y/B. But in the transmission of light through a prism, though the 

 wave which is propagated by normal vibrations were incapable itself of 

 affecting the eye, yet it would be capable of giving rise to an ordinary 

 wave of light propagated by transverse vibrations, except in the ex- 



A A 



treme cases where ■== = 0, or — = a very large quantity ; which, for 



the sake of simplicity, may be regarded as infinite; and it is not diffi- 

 cult to prove, that the equilibrium of our medium would be unstable 



A 4 



unless j5 > - . We are therefore compelled to adopt the latter value of 



-=:, and thus to admit that in the luminiferous ether, the velocity of 



transmission of waves propagated by normal vibrations, is very great 

 compared with that of ordinary light. 



