THE 



LONDON AND EDINBURGH 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[THIRD SERIES.] 



DECEMBER 1832. 



T' 



LXX. On the Variations 'which Temperatiire j^foduces in the 

 Double Refraction of Cri/stah. By Frederick Rudberg, 

 Professor of Physics in the University cfUpsal*. 

 'HE researches of M. Mitscherlich having demonstrated 

 that the angles of crystals which do not belong to the 

 regular system, change their magnitude with the temperature, 

 and that the dilatation is consequently different, according to 

 the principal directions of these bodies, or according to their 

 axes of crystallization, there was reason to believe that the 

 double refraction also would vary with the temperature. The 

 existence of this variation was afterwards established by ul- 

 terior researches, which M. Mitscherlich, in a manner as simple 

 as it was ingenious, made by the method of interferences, by 

 observing the compensation effected by crossing plates of cry- 

 stals at different temperatures. By this method, however, we 

 obtain only the ratio between the mean double refraction of 

 the crystal in a cold and in a heated state, without being able 

 to determine how much the refraction of each of the two rays 

 into which the light divides itself, has separately varied with 

 the difference of temperature. In order to decide this question, 

 we must obviously determine directly the refraction at a high 

 temperature ; and the following are the results of such an in- 

 quiry, made with rock crystal^ calcareous spar, and arragonite. 

 The experiments were made in the same place, and by 

 means of the same instruments and the same prisms, as my 

 former cxperimentsf on the refraction of the same minerals 

 at the temperature of the air; and for this reason I do not 



* Communicated iiy the Author. 



•j- Sec our present volume, p. 1, and 1.36,— Edit. 



Third Series. Vol. 1. No. G. Dec. 1832. 3 G 



