LIGHT. 129 



light, so light must have been made, at least 

 among other ends, for the eye. 



1 . We must expect to comprehend imperfectly 

 only the mechanism of the elements. Still, we 

 have endeavoured to show that in some instances 

 the arrangements by which their purposes are 

 affected, are, to a certain extent, intelligible. In 

 order to explain, however, in what manner light 

 answers those ends which appear to us its princi- 

 pal ones, we must know something of the nature 

 of light. There have, hitherto, been, among men 

 of science, two prevailing opinions upon this sub- 

 ject: some considering light as consisting in the 

 emission of luminous particles ; others accounting 

 for its phenomena by the propagation of vibra- 

 tions through a highly subtle and elastic ether. 

 The former opinion has, till lately, been most 

 generally entertained in this country, having been 

 the hypothesis on which Newton made his calcu- 

 lations ; the latter is the one to which most of 

 those persons have been led, who, in recent times, 

 have endeavoured to deduce general conclusions 

 from the newly discovered phenomena of light. 

 Among these persons, the theory of undulations is 

 conceived to be established in nearly the same 

 manner, and almost as certainly, as the doctrine 

 of universal gravitation ; namely, by a series of 

 laws inferred from numerous facts, which, pro- 

 ceeding from different sets of phenomena, are 

 found to converge to one common view ; and by 



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