EPOCH OF YOUNG AND FRESNEL. 437 



to a considerable extent by various inquirers 13 ; 

 and the opinions at which these persons arrived, 

 they found that they could express most readily, 

 in consistency with the reigning chemical views, by 

 assuming the materiality of light. It is, however, 

 clear, that no reasonings of the inevitably vague 

 and doubtful character which belong to these por- 

 tions of chemistry, ought to be allowed to interfere 

 with the steady and regular progress of induction 

 and generalization, founded on relations of space 

 and number, by which procedure the mechanical 

 sciences are formed. We reject, therefore, all these 

 chemical speculations, as belonging to other sub- 

 jects; and consider the history of optical theory 

 as a blank, till we arrive at some very different 

 events, of which we have now to speak. 



13 As Scheele, Selle, Lavoisier, De Luc, Richter, Leonhardi, 

 Gren, Girtanner, Link, Hagen, Voigt, DC la Metherie, Scherer, 

 Dize, Brugnatelli. See Fischer, vii. p. 20. 



