the Luminiferous Ether. .227 



to remain constant. If we assume the elasticity to remain 

 constant, we have that the density of the ether must be this 

 number of times less than the density of the air. The neces- 

 sity for the existence of the ether therefore is, that we 

 require a body whose elasticity shall be this number of times 

 greater, or whose density shall be this number of times less, than 

 that of the air. It is hardly necessary to add that we know 

 of no such body in nature ; and since we cannot conceive of 

 motion without having something moved, we invent the hypo- 

 thetical substance ether, which shall be the vehicle of our wave- 

 motion. But have we not been too eager to invent ? have we 

 thoroughly satisfied ourselves that matter itself (t. e. ordinary 

 matter) is incapable of transmitting the vibratory movement ? 

 In attempting to answer these questions, we have first to show 

 that the theory of the constitution of the luminiferous ether as 

 at present held is untenable ; and, secondly, we must endeavour 

 to show that the particles of matter themselves are capable of 

 taking up and transmitting the wave-motion. 



Difficulties in the Conception of the Ether. 



The difficulties which one meets with in the belief in the 

 existence of this substance may be divided into two classes — 

 those founded on theoretical considerations, and those founded 

 on experimental evidence. We will first consider the former. 



In the preceding portion we have stated that the ether must 

 possess enormous elasticity and very little density. This is 

 the view usually accepted : thus Tyndall says, " it is assumed 

 to be of both extreme elasticity and of extreme tenuity." Now, 

 if this be the case, it of course follows that this ether will be 

 distributed in space in the same way that matter is distributed ; 

 viz. it will accumulate around the celestial bodies, and the 

 greater the mass of the body the greater the atmosphere (if 

 we may use the term) of ether surrounding it. We ought, 

 therefore, to find that a gradual increase of refractive power 

 occurred as we approached a celestial body. In the compa- 

 ratively few cases in which this can be tested it is found to be 

 the case ; but it is, I believe, universally attributed to the in- 

 fluence of the atmosphere. But we must consider this tenuity 

 to be so great that it is impossible for us to recognize it by 

 any of our balances. For if we carefully weigh a piece of a 

 transparent substance, such as glass, and then grind it to 

 powder (in which process we must liberate some of the ether 

 which is held between the molecules), and weigh the powder, 

 we obtain the same weight as before, showing that the ether 

 we have lost had not sufficient weight to affect the balance. 

 Some of the upholders of the undulatory theory, however, take 



T2 



