140 TERRESTRIAL ADAPTATIONS. 



may not interrupt the progress of our argument, 

 we shall refer to other works for the reasonings 

 which appear to lead to this conclusion. But 

 whether heat, electricity, galvanism, magnetism, 

 be fluids ; or effects or modifications of fluids ; 

 and whether such fluids or ethers be the same 

 with the luminiferous ether, or with each other ; 

 are questions of which all or most appear to be at 

 present undecided, and it would be presumptuous 

 and premature here to take one side or the other. 



The mere fact, however, that there is such an 

 ether, and that it has properties related to other 

 agents, in the way we have suggested, is well 

 calculated to extend our views of the structure of 

 the universe, and of the resources, if we may so 

 speak, of the power by which it is arranged. 

 The solid and fluid matter of the earth is the 

 most obvious to our senses ; over this, and in its 

 cavities, is poured an invisible fluid, the air, by 

 which warmth and life are diffused and fostered, 

 and by which men communicate with men : over 

 and through this again, and reaching, so far as 

 we know, to the utmost bounds of the universe, 

 is spread another most subtle and attenuated 

 fluid, which, by the play of another set of agents, 

 aids the energies of nature, and which, rilling all 

 parts of space, is a means of communication with 

 other planets and other systems. 



There is nothing in all this like any material 

 necessity, compelling the world to be as it is and 



