324 Mr KELLAND, ON THE TRANSMISSION OF LIGHT 



to establish the law in question, afforded strong presumptive evidence 

 in its favour; not confined to the action of the particles of ether, but 

 extending to those of air, and giving normal vibrations in the latter 

 instance as the cause of the phenomena of sound. 



All the investigations were, however, confined to a perfectly sym- 

 metrical medium, on which account the results were limited to non- 

 crystallized substances. 



My object at present is to complete the view I have taken of the 

 subject, by extending analogous artifices of simplification to particles 

 arranged not in a perfectly symmetrical manner, but symmetrical only 

 with respect to three planes at right angles to one another. 



In entering on this subject, I must remind you that I take for 

 granted the law of the inverse square of the distance as established ; 

 and the novelty which is presented by the present view of the subject 

 arises from the difference in the form of the force corresponding to a 

 disturbance in the normal direction, from that put in play by a dis- 

 turbance in the transverse direction. 



I have limited my operations to one series of particles, from the 

 circumstance that the form is not altered by introducing another series, 

 provided the latter act on the former, and are themselves subject to 

 the action of the former. The results arising from the combination 

 of two sets, I have proved to be the sums or differences of the results 

 arising from each set respectively. 



It is true that the action of material particles has been totally 

 omitted, the material particles being supposed to exert on tliose of 

 ether an influence by wliich they themselves are not reciprocally 

 affected. My reason for this omission is, tliat such influence will not 

 affect the motion in a non-crystallized medium, (see Trans. Camb. Phil. 

 Sac. Vol. VI. p. 244.) and, consequently, will not materially affect it in a 

 crystallized one. The charge which has lately been brought against the 

 hypothesis which M. Cauchy and others have adopted, is, that it omits 

 altogether the action of the particles of matter. 



