1 48 Mr. Delaval on the Caufe of the 



In proportion as the Principles of any Science 

 are unknown or mifconceived, the advancement 

 of the Arts and Manufaftures, which depend on 

 them, mufl: of courfe be impeded : for, without 

 thofe guides, no addition or improvement can 

 be attained, except fuch as arife from mere acci- 

 dental obfervation. 



But when fcientific Principles are difclofed to 

 the Artift, he becomes enabled to draw, from 

 thofe original fources, an ample ftore of ufeful 

 inventions, by which his Art is conflantly en- 

 riched ; and from thence confiderable advantages 

 may be derived. And thus the fpeculative Sci- 

 ences, by their ^xtenfion to pradical purpofes, 

 become objedls of great public utility. 

 (; The truth of this obfervation is, in no in- 

 ilance, more confpicuous, than when applied 

 to the Science of Optics, and to the Arts and 

 Manufadures, which are conneded with, and 

 dependent upon it. For, the invention and 

 improvement of the feveral operations, which 

 owe their rife to that Science, appear to have 

 kept an equal pace with the philofophical dif- 

 coveries, by which they were fuggefted : and 

 their progrefs feems to have been conftantly 

 retarded, in proportion as the correfpondent 

 branches of the parent Science have remained 

 in a ftate of deficiency or imperfedion. 



The experiixients and obfervations, which have 

 •been made by means of Tranfparcnt Colourlefs 



Subftances, 



