THE 



LONDON AND EDINBURGH 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[THIRD SERIES.] 



JULY 1832. 



I. On the Refraction of the differently-coloured Rays in 

 Crystals with one and two Axes of Double Refraction. By 



M. RUDBEKG*. 



A S the remarkable discovery of Fraunhofer of the dark rays 

 '^^ in the spectrum gives an unexpected degree of precision 

 to researches on the refraction of coloured light, it becomes 

 interesting to determine by this accurate method the indices 

 of refraction. With the view principally of constructing more 

 perfect achromatic object-glasses, Fraunhofer himself deter- 

 mined the refraction of the differently-coloured rays for several 

 kinds of flint and crown glass, and also for some other sub- 

 stances that have simple refractionf. But for doubly refract- 

 ing crystals similar researches are entirely wanting, which 

 might show in general how the double refraction varies with 

 different colours, and how this variation produces the different 

 inclination of the optic axes which Mr. Herschel has* observed 

 for the differently-coloured rays in crystals with two axes. 

 Besides, an inquiry into the double refraction of coloured 

 light would add to the small number of accurate determina- 

 tions of dispersion which we owe to Fraunhofer. 



In order to measure accurately the deviation of the ray re- 

 fracted by a prism, as well as its own refracting angle, I used 

 a repeating circle constructed by Lenoir, which Swanberg 

 had used in tlie measurement of the degree of the meridian 

 in Lapland, and which being divided centesimaliy gave im- 



• From the Annalcs de C/iimie et de Physique, torn, xlviii. p. 225. 

 t See Phil. Mag. and Annals, N.S. vol. ii. p. 401.— Edit. 



Third Series. Vol. J. No. 1. July \S32. B 



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