REPEATING GOXIO3IETER. 



161 



brought to perfection without at the same time inducing 

 a corresponding amelioration in the latter. In propor- 

 tion as the crystallographic ideas of Hau'y acquired more 

 exactness, it was found necessary to employ, for the meas- 

 urement of the angles of the crystals, methods of increas- 

 ing precision. 



^Vollaston supplied this want by the invention of the 

 reflective goniometer which bears his name.* Mains 



hesitated fully to adopt the idea, after it had occurred to him as the 

 only mode of representing polarization, on the ground of being unable 

 to reconcile it with mechanical notions; and this more precisely as 

 to the notion of transverse vibrations alone being produced, which 

 constituted this theory in all its simplicity; whereas Young had (as 

 we have just seen) believed both these and longitudinal vibrations to 

 coexist. To establish 1liis point, he expressly says, was the main dif- 

 ficulty which embarrassed him.} Translator. 



* The essential principle of the reflective goniometer of "\Vollaston 

 is extremely simple, and consists in this : a piece of crystal or any 



1 Ann. de Chimie, 1831, torn. xvii. p. 184. 



