840 M. G. Wertheim on the double Refraction 



attentively, and especially that of luminous meteors, expressed the 

 opinion, at a lecture delivered at the Radcliffe Library, on the 

 24th June, 1847, that there exists a connexion between aerolites 

 and luminous meteors i and that such small bodies may circulate 

 in the solar system, though probably in small numbers, unless 

 truly planetary, or as satellites of some of the larger planets, as 

 of the earth*. 



[To be continued.] 



XLIY. On the double Refraction temporarily produced in Iso- 

 tropic Bodies. By M. G. Wertheim. 



[Concluded from p. 261.] 



Theory, 



LET the quantities H, Lo, La, C, E, d, and \ be defined as 

 above. Further, let S be the linear change which takes 

 place in the direction of the force, the sign of which we will 

 assume to be positive or negative according as the force P pro- 

 duces a lengthening or a shortening ; the velocity of the light 

 in air; Oo and 0^ the velocities, ordinary and extraordinary, in 

 the substance, which has become temporarily birefractive. 



According to the law of the ratios of linear changes, the three 

 dimensions of the parallelepiped, during the action of the force 

 P, have become 



H(l + S), Lo(l-|), La(l-|). 



The two rays have to pass over the length Lof 1— q), conse- 

 quently their difference of path d, after issuing from the parallel- 

 epiped, is proportional toLofl— ^jfTt — ^j and to the linear 

 change B; we have thus 



-"('-Dfi-s) 



The value of 8 can always be determined by means of the coeffi- 

 cient of mechanical elasticity; for pretty considerable charges 



* It haa been shown by Erman and Pierce (See American Philosophical 

 Transactions for 1841), that the influence of the earth's attraction on me- 

 teoric bodies, approaching near that planet, with planetary velocity, is not 

 considerable ; at least not equal to any errors of observation in a calculation 

 of their orbits. It has also been proved that the maximum velocity of a 

 meteoric body, revolving, as a satellite of the earth, cannot exceed 5^ miles 

 in a second, whereas the average velocity of these bodies is about fifteen 

 miles per second. 



