THE ETHER DRIFT. 



By AUGUSTUS TROWBRIDGE. 



(Read April 22, iQio.) 



At one time in the course of the development of physical science 

 there were almost as many ethers postulated as there were phe- 

 nomena to be explained. " Ethers were invented for the planets 

 to swim in, to constitute electric atmospheres and magnetic effluvia, 

 to convey sensations from one part of the body to another, till all 

 space was filled several times over with ethers" (J. C. Maxwell). 



Of all these ethers the only one which has survived to our day 

 is that of Huygens which is, so to speak, working over-time in 

 that it has to serve the electrician as well as the optician and it is 

 rather disheartening to think that after more than one hundred 

 years of unremitting labor all that we really know of its properties 

 is this — it transmits any electro-magnetic disturbance with the speed 

 of three hundred million meters per second. 



When we admit the hypothesis of the ether with this property 

 the question arises as to the nature of the mechanical bonds between 

 ether and matter — there are of course three possibilities — when 

 matter is in motion either the ether moves with it completely, or 

 it is partially entrained or it is not entrained at all. 



The simplest of these three possibilities is perhaps the first — 

 that the ether is completely entrained by the moving matter — it is 

 the simplest hypothesis because it would mean that matter, once 

 associated with a given quantity of ether, remained so forever and 

 if this were the case we might hope to explain matter in terms of 

 the ether indissolubly associated with it. Unfortunately the cele- 

 brated experiment of Fizeau on the change of velocity of light with 

 and against a stream of moving transparent matter rules out this 

 simplest hypothesis of complete entrainment and leaves us the 

 choice of an ether which is partially entrained by moving matter or 

 one which is a rest absolutely and not entrained at all. 



