416 HISTORY OF OPTICS. 



and did influence, materially and beneficially, the 

 subsequent progress of Optics towards a connected 

 theory. 



We must now trace this progress; but before 

 we proceed to this task, we will briefly notice a 

 number of optical phenomena which had been col- 

 lected, and which waited for the touch of sound 

 theory to introduce among them that rule and order 

 which mere observation had sought for in vain. 



