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SCIENCE 



[N. S. Vol. XXXVIII. No. 977 



tant contributions which they have made 

 to the subject-matter of this discussion. 



Why is so much importance attached to 

 radiation? Because it is the best-known 

 and longest-studied link between matter 

 and ether, and the only property we are ac- 

 quainted with that affects the unmodified 

 great mass of ether alone. Electricity and 

 magnetism are associated with the modifi- 

 cations or singularities called electrons: 

 most phenomena are connected still more 

 directly with matter. Radiation, however, 

 though excited by an accelerated electron, 

 is subsequently let loose in the ether of 

 space, and travels as a definite thing at a 

 measurable and constant pace — a pace in- 

 dependent of everything so long as the 

 ether is free, unmodified and unloaded by 

 matter. Hence radiation has much to 

 teach us, and we have much to learn con- 

 cerning its nature. 



How far can the analogy of granular, 

 corpuscular, countable, atomic or discon- 

 tinuous things be pressed? There are 

 those who think it can be pressed very far. 

 But to avoid misunderstanding let me 

 state, for what it may be worth, that I 

 myself am an upholder of ultimate con- 

 tinuity, and a fervent believer in the ether 

 of space. 



We have already learned something 

 about the ether; and although there may 

 be almost as many varieties of opinion as 

 there are people qualified to form one, in 

 my view we have learned as follows : 



The ether is the universal connecting 

 medium which binds the universe together, 

 and makes it a coherent whole instead of a 

 chaotic collection of independent isolated 

 fragments. It is the vehicle of transmis- 

 sion of all manner of force, from gravita- 

 tion down to cohesion and chemical affin- 

 ity ; it is therefore the storehouse of poten- 

 tial energy. 



Matter moves, but ether is strained. 



What we call elasticity of matter is only 

 the result of an alteration of configuration 

 due to movement and readjustment of par- 

 ticles, but all the strain and stress are in 

 the ether. The ether itself does not move, 

 that is to say it does not move in the sense 

 of locomotion, though it is probably in a 

 violent state of rotational or turbulent mo- 

 tion in its smallest parts; and to that mo- 

 tion its exceeding rigidity is due. 



As to its density, it must be far greater 

 than that of any form of matter, millions 

 of times denser than lead or platinum. 

 Yet matter moves through it with perfect 

 freedom, without any friction or viscosity. 

 There is nothing paradoxical in this : vis- 

 cosity is not a function of density; the two 

 are not necessarily connected. When a 

 solid moves through an alien fluid it is true 

 that it acquires a spurious or apparent 

 extra inertia from the fluid it displaces; 

 but in the case of matter and ether, not 

 only is even the densest matter excessively 

 porous and discontinuous, with vast inter- 

 spaces in and among the atoms, but the 

 constitution of matter is such that there 

 appears to be no displacement in the ordi- 

 nary sense at all; the ether is itself so 

 modified as to constitute the matter in some 

 way. Of course that portion moves, its 

 inertia is what we observe, and its amount 

 depends on the potential energy in its 'as- 

 sociated electric field, but the motion is not 

 like that of a foreign body, it is that of 

 some inherent and merely individualized 

 portion of the stuff itself. Certain it is 

 that the ether exhibits no trace of viscosity.^ 



Matter in motion, ether under strain, 

 constitute the fundamental concrete things 

 we have to do with in physics. The first 



' For details of my experiment on this subject 

 see Phil Trans. Soy. Soo. for 1893 and 1897; or a 

 very abbreviated reference to it, and to the other 

 matters above mentioned, in my small book, "The 

 Ether of Space." 



