136 TERRESTRIAL ADAPTATIONS. 



tion of light by means of a subtle medium, leads 

 necessarily to the extraordinary collection of 

 properties which have recently been discovered ; 

 and, at any rate, its propagation by the trans- 

 verse vibrations of such a medium does lead 

 inevitably to these results. 



Leaving it therefore to future times to point 

 out the other reasons (or uses if they exist) of 

 these newly discovered properties of light, in 

 their bearing on other parts of the world, we may 

 venture to say, that if light was to be propagated 

 through transparent media by the undulations of 

 a subtle fluid, these properties must result, as 

 necessarily as the rainbow results from the un- 

 equal refrangibility of different colours. This 

 phenomenon and those, appear alike to be the 

 collateral consequences of the laws impressed 

 on light with a view to its principal offices. ' 



Thus the exquisitely beautiful and symmetrical 

 phenomena and laws of polarization, and of crys- 

 talline and other effects, may be looked upon as 

 indications of the delicacy and subtlety of the 

 mechanism by which man, through his visual 

 organs, is put in communication with the exter- 

 nal world ; is made acquainted with the forms 

 and qualities of objects in the most remote regions 

 of space ; and is enabled, in some measure, to 

 determine his position and relation in a universe 

 in which he is but an atom. 



4. If we suppose it clearly established that 

 light is produced by the vibrations of an ether, 



