PHYSICAL AND LITERARY. 8i^ 



Tcally move with different velocities, our. 



theory of light will be ftill farther improved ; 



as the different refrangibility can be thence 



mechanically explained. 



The whole fyftem of Nature is one im- 

 menfe feries of caufes and effects, whofe be- 

 ginning and end are equally hid^ in- the 

 depths of infinity. Only a fmall, a very 

 fmall portion of it, comes under our imme- 

 diate obfervation ; being expofed alike to 

 the fight and other fenfes of all mankind. 

 Almoft every phcenomemn is, at once, the 

 caufe of manifold effedls ; and one effedr, 

 among many, of a fuperior caufe. The bu- 

 finefs of Science is to extend our views, by 

 unfolding the latent caufes which exift in 

 Nature ; and thence explaining their mani- 

 feft effeds. The difcovery of one fuch 

 real caufe, unknown before, if it be of ge- 

 neral or very extenfive influence, as that of 

 univerfal gravity, is to be efteemed a great 

 advancement of natural philofophy. To 

 undervalue fuch a difcovery, as fome have 

 done, becaufe the caufe of that caufe can- 

 not 'yet be affigned, is highly abfurd : fince 

 the fame objedion muff for ever ly againft 



Vol. II. M all 



