179 



VIII.— On the Equilibrium and Motion of an Elastic Solid. By the Rev. John 

 H. Jellett, Fellow of Trinity College, and Professor of Natural Philosophy 

 in the University of Dublin. 



Bead January 28, 1850. 



1. 1 HE problem which forms the subject of the present Memoir has already, at 

 various times, occupied the attention of mathematicians. Although much of the 

 interest which it has excited is due to its connexion with the undulatory theory 

 of light, the importance of the problem itself, considered as a branch of rational 

 mechanics, is fully admitted; and more than one writer has treated of it without 

 regard to the real or supposed existence of a luminous ether. Nor can it, I 

 think, be doubted, that such a distinction between the rational and the physical 

 science, is in accordance with the dictates of just philosophy. The rational 

 science woidd still be real, even though the existence of the ether were (if that 

 were possible) disproved ; and the admitted reality of the several solid and fluid 

 bodies which are found in nature gives us, in such cases, the means of testing 

 by experiment the accuracy of the laws arrived at. " Whatever theoretic ob- 

 jections," says Mr. Haughton, " may be made to the application of the theorj' 

 of elastic media to optics, none such exist as to its application to solid and fluid 

 bodies. The mathematical investigations which, in the case of hght, must be 

 hj'pothetical, are, in the case of solid and fluid bodies, essentially positive, and 

 may be made the subject of direct experiment. A general inquiry into the 

 laws of elastic media is an interesting application of rational mechanics ; and 

 although it must necessarily include cases purely hypothetical, it is not, there- 

 fore, to be considered unimportant." * 



* Transactions of the Eoyal Irish Academy, Vol. xxii. Part i. p. 97. 



VOL. xxn. 2 B 



