478 Dr. G. J. Stoney on Texture in Media. 



It thus appears that the distinction between different parts, 

 which is implied by the term density, does not exist* in the 

 elemental aether, and that in it the element of volume is the 

 element of mass. There is, accordingly, no such physical 

 quantity as density in the dynamics of the ultimate motions 

 of the elemental aether. It is only when accumulations of 

 these primary motions are lumped together, and where what we 

 are investigating is merely the drifting about of these accumu- 

 lations — it is only in this branch of dynamics that we find the 

 need and the advantage of the conception of density as a 

 substitute for having to take separately into consideration some 

 of the motions that are really going on. In fact, if any such 

 hypothesis as Sir William Thomson's is true, the density of a 

 lump of iron, i. e. the coefficient by which the elements of its 

 volume have to be multiplied in order to get their masses, is 

 nothing but a mere function of the primary or elemental motions 

 prevailing in that portion of spaced and which alone make that 

 portion of space differ from one in which other elemental 

 motions are going on. 



aspect — is of either of these kinds ; and accordingly it is improbable that 

 empty coreless vortices are any part of real Nature. This is a kind of 

 objection which may raise an improbability, even a great improbability; 

 but we should be rash to rely on it as finally decisive, for the reality of 

 things is not limited by our way of conceiving them. 



The objection, such as it is, would not lie against the presence in 

 nature of coreless vortices lined with a vortex sheet and filled in with a 

 part of the medium devoid of rotational motion ; but such vortices would 

 in some respects behave differently from empty coreless vortices. 



* This conclusion is confirmed by an important ontological proposition 

 which is susceptible of demonstration, viz. that nothing that we suppose 

 to exist in nature can be " real," unless it is a syntheton of perceptions 

 actual, potential, or conceivable. Thus, motions and space relations may 

 be " real," for they are such syntheta ; but a " thing to move " is not real 

 except in those cases in which the motion we are considering is the 

 drifting motion of volumes within which subsidiary motions prevail. In 

 such cases the subsidiary motions are often thought of, and may, perhaps 

 without objection, be spoken of as a thing that moves. 



t That is, on the supposition that the luminiferous aether is of uniform 

 texture throughout its whole extent, as seems to be the case. If, how- 

 ever, the fact be otherwise, we must regard the density of the iron as a 

 function both of the elemental motions pervading its volume and of the 

 elemental motions in the adjoining part of the luminiferous aether. The 

 density of the iron would then depend on its situation in the material 





