FOURTH REPORT — 1834. 



general theory of light ; for these equations must necessarily 

 express the characteristic properties of the vibrating medium. 

 In this point of view their discussion becomes a subject of the 

 highest interest ; and it is probable that the important conclu- 

 sions of which we have yet to speak may in this manner be 

 confirmed and extended. 



These conclusions are contained in a memoir presented to the 

 French Academy by M. Lam^, in the spring of the present 

 year*; and in which the author has proposed to determine the 

 laws according to which the molecules of bodies act on those of 

 the ether, and the molecules of the ether on one another. Set- 

 ting out from the existence of transversal vibrations, as esta- 

 blished 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 

 hod}/. Assuming the property of transversal vibrations noticed 

 by Fresnel, and more explicitly stated by M. Poisson, — namely, 

 that they are propagated ivithout any attendant change of 

 density, — M. Lame then seeks the conditions to be satisfied by 

 the function, which represents the mutual action of the mole- 

 cules 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 equa- 

 tion 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 sigyi 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 

 molecule of the body, around which the ether is distributed in 

 spherical 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 re- 

 sult, that the mean density of the ether is less in the former j 

 or that the action of the molecules of these bodies on those of 



* " Memoire surles Lois de I'Equilibre de I'Ether dans les Corps diaphancs." 

 A full account of this paper is given in the Annales de Chimie for March. The 

 memoir itself is not yet published. 



