296 MODERN SCIENCE READER 



Not till last year, however, did I realize what the density 

 of the ether must really be, 1 compared with that modifica- 

 tion of it which appeals to our senses as matter, and which, 

 for that reason, engrosses our attention. I will return to 

 this part of the subject directly. 



Is there any other function possessed by the ether, which, 

 though not yet discovered, may lie within the bounds of pos- 

 sibility for future discovery ? I believe there is, but it is too 

 speculative to refer to, beyond saying that it has been urged 

 as probable by the authors of The Unseen Universe, and 

 has been tentatively referred to by Clerk Maxwell thus: 



Whether this vast homogeneous expanse of isotropic matter is 

 fitted not only to be a medium of physical interaction between dis- 

 tant bodies, and to fulfil other physical functions of which, perhaps, 

 we have as yet no conception, but also ... to constitute the material 

 organism of beings exercising functions of life and mind as high or 

 higher than ours are at present is a question far transcending the 

 limits of physical speculation. 



And there for the present I leave that aspect of the 

 subject. 



I shall now attempt to illustrate some relations between 

 ether and matter. 



The question is often asked: Is ether material? That is 

 largely a question of words and convenience. Undoubtedly 

 the ether belongs to the material or physical universe ; but 

 it is not ordinary matter. I should prefer to say it is not 

 "matter" at all. It may be the substance or substratum 

 or material of which matter is composed, but it would be 

 confusing and inconvenient not to be able to discriminate 

 between matter on the one hand, and ether on the other. 

 If you tie a knot on a bit of string, the knot is composed of 

 string, but the string is not composed of knots. If you 

 have a smoke or vortex-ring in the air, the vortex-ring is 

 made of air, but the atmosphere is not a vortex-ring; and 

 it would be only confusing to say that it was. 



The essential distinction between matter and ether is that 



J See the Philosophical Magasine for April, 1907. 



