134 TERRESTRIAL ADAPTATIONS. 



exhibit the most remarkable differences when 

 they pass through certain crystals, but manifest 

 no discoverable difference in their immediate im- 

 pression on the eye. We have, therefore, here a 

 number of laws of light, which we cannot per- 

 ceive to be established with any design which 

 has a reference to the other parts of the universe. 

 Undoubtedly it is exceedingly possible that 

 these differences of light may operate in some 

 quarter, and in some way, which we cannot 

 detect ; and that these laws may have purposes 

 and may answer ends of which we have no sus- 

 picion. All the analogy of nature teaches us a 

 lesson of humility, with regard to the reliance we 

 are to place on our discernment and judgment as 

 to such matters. But with our present know- 

 ledge, we may observe, that this curious system 

 of phenomena appears to be a collateral result of 

 the mechanism by which the effects of light are 

 produced ; and therefore a necessary conse- 

 quence of the existence of that element of which 

 the offices are so numerous and so beneficent. 



The new properties of light, and the specula- 

 tions founded upon them, have led many persons 

 to the belief of the undulatory theory ; which, as 

 we have said, is considered by some philosophers 

 as demonstrated. If we adopt this theory, we 

 consider the luminiferous ether to have no local 

 motion : and to produce refraction and reflexion 

 by the operation of its elasticity alone. We must 

 necessarily suppose the tenuity of the ether to be 



