X. On the Optical Properties of Sulphuret of Carbon, Carbo- 

 nate of Barytes, and Nitrate of Potash, with Inferences 

 respecting the Structure of Doubly Refracting Crystals, 

 By David Brewster, LL. D, F, R. S. Edin. & F. A. S. E. 



i 



(Bead February 7. 1814. J 



N examining the changes which light undergoes during its 

 passage through transparent bodies, we not only receive in- 

 formation respecting the properties of that mysterious agent ; 

 but we are in some measure made acquainted with the compo- 

 sition of the substances themselves, and with the manner in 

 which their ingredients are combined. The optical phenome- 

 na, therefore, which bodies exhibit in their action upon light, 

 are so many tests, to which the philosopher may have recourse 

 either in supplying the place of chemical analysis, or in cor- 

 recting and modifying its results. A difference in the optical 

 properties of two bodies, is generally an infallible indication of 

 a difference in their elementary principles ; and whatever con- 

 fidence we may place in the skill of the chemist, or in the ac- 

 curacy of his methods, the mind can never rest satisfied with 

 the results of an analysis which is directly opposed by optical 

 phenomena. 



Vol. VII, P. II. O o j t 



