I low w !•; SHI':. h;.") 



od_m' is })r()val)lc. ( )iii- liuls ivucli back (jiily to a ccrtiiin 

 j)oint — never to the hejjfinning. Hciencc is constantly pusli- 

 in<:,- hack lur line of priniordial data, Ijiit it is hardly 

 l)robablc ibaL the tiine will ever come when the essence, so 

 to speak, of any nianifestiition in natun; can be demonstrated. 

 Nature's Jaws, we can study and unravel — the origin of 

 these laws will probably ever remain an unsolved mv.stery. 

 The nature of light is one of these mysteries which can be 

 apj)roaclied by speculation alone, and as none of the po.'*- 

 tulates need be demonstrated, the Held for the exerci.se of 

 the speculative faculty is j)ractically unlimited. Newton 

 adopted his corpuscular theory, not because he could dem- 

 onstrate the existence of the corpuscles, but because by so 

 doing he thought he was explaining the phenomena with 

 the least violence to known laws and the scientific princi])les 

 of the time. 



There was one great original mind, however, which came 

 after him, that refused to accept any theory on any other 

 man's authority, however great that man might be. This 

 was Thomas Young, probably the most universal genius 

 England has given to the world. Thomas Young did not 

 consider the corpuscular theory of light satisfactory, a!id pro- 

 ceeded to revive and modify what is called the undulatory 

 theory, which had been broached by Huygens Ijefore the time 

 of Newton. By this theory he was enabled to account in a 

 more consistent and .satisfactory manner for some of the 

 manifestations of light than could be done by the corpus- 

 cular theory of Newton. This undulatory hypothesis as pro- 

 mulgated by Young, is the basis of all modern speculations 

 as to the nature and laws of light. In common with all 

 theories dealing with the essential nature of things, it draws 

 largely upon our credulity, and asks us to accept as data 

 as many postulates which have never been and which can, 

 from the very nature of the case, never be i)roven as does 

 tlie corpuscular theory of Newton. 



In the first place, we are recjuircd to su})i»ose the existence 

 of an ether which is coextensive with the universe. It tills 

 the interstellar space to the farthest fixed star, whose distance 



