126 REPORT ON PHYSICAL OPTICS. 



in which the author has proposed to determine the laws accord- 

 ing to which the molecules of bodies act on those of the ether, 

 and the molecules of the ether on one another. Setting out from 

 the existence of transversal vibrations, as established by the fact 

 of the non-interference of rays oppositely-polarized, the author 

 supposes a disturbance of the ether to take place in vacuum that 

 is, in a space devoid of all ponderable matter, and proceeds to 

 consider what will be the result when that disturbance reaches the 

 ether contained in a transparent body. Assuming the property of 

 transversal vibrations noticed by Fresnel, and more explicitly 

 stated by M. Poisson namely, that they are propagated without 

 any attendant change of density, M. Lame then seeks the conditions 

 to be satisfied by the function, which represents the mutual action 

 of the molecules of the ether and those of the solid body, in order 

 that this property may subsist. Introducing, accordingly, this 

 principle into the partial differential equations, which express the 

 laws of the vibratory movement generally, he arrives finally at an 

 equation of condition, from which he concludes that " the action 

 of ponderable matter on the ether varies in the inverse ratio of the 

 square of the distance ; and that the elasticity of the ether itself is 

 proportional to its density." 



In order to determine the sign of this action that is to say, 

 whether it is attractive or repulsive, it is necessary to integrate 

 the differential equations. After certain transformations of these 

 equations tending to facilitate their examination, he obtains their^ 

 integral in the case of a single spherical and homogeneous mole- 

 cule of the body, around which the ether is distributed in spheri- 

 cal shells. The conclusions deduced from this case being combined 

 with the established fact, that the velocity of light is less in 

 transparent bodies than in vacuum, he arrives at the result, that 

 the mean density of the ether is less in the former, or that 

 the action of the molecules of these bodies on those of the ether is 

 rr-pukive. M. Lame concludes also from the examination of the 

 same case, that the retardation of the vibratory motion, in pene- 

 trating into a dense body, will be greater, the less the length of 

 an undulation, so that the refraction will be greater for waves of 

 shorter length. This he conceives to be the true explanation of 

 the phenomenon of dispersion. 



M. Lame has likewise endeavoured to connect the phenomena 

 of double refraction with an assumed constitution of the ethereal 



