THE 

 LONDON, EDINBURGH and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SOIENOE. 



[FOURTH SERIES.] 



OCTOBER 1854. 



XXXIII. On the douhh Refraction temporarily produced in Iso* 

 tropic Bodies. J5?/ M. G. Wertheim*. 



[With a Plate.] 



Description of the Apparatus and manner of operation. 



IN a homogeneous body submitted to compression in one 

 direction only, the molecules are caused to approach each 

 other in this direction, and they are forced asunder in the two 

 perpendicular directions : the reverse takes place when we sub- 

 stitute traction for compression. The relations between simul- 

 taneous dilatations and compressions, have been actually ascer-* 

 tained to a degree of exactitude equal to that of which experi- 

 mental questions are usually susceptible. This mechanical effect 

 is accompanied by an optical one, which we can observe in trans- 

 parent bodies, and which is explained by the diminution of the 

 elasticity of the sether in the direction of the mechanical com- 

 pression, and its augmentation in the direction of dilatation. 



It is proposed to discover the relations subsisting between the 

 force applied to a body of known dimensions and the two species 

 of effects produced, whatever may be the mechanical or optical 

 elasticities of the bodies operated on, provided that they are con- 

 stant in all directions. In other words, the two surfaces of elas- 

 ticity being spheres in the natural state of the body, it is pro- 

 posed to determine the form and position of the two surfaces 

 after the application of an external force, which, by pressure or 

 by traction, acts in a uniform manner upon the whole body ill 

 one of its dimensions. 



* Extracted from a separate Pamphlet published by Mallet-Bachelier. 

 Paris, 1854. 



Phil Mag, S. 4. Vol. 8. No. 52. Oct, 1854. R 



