MATTER 271 



become a current symbol of scientific shorthand. Nor is 

 the reason far to seek ; we desire to construct, if possible, 

 the prime-atom from an ether-motion, but our conceptions 

 of the ether are at present very ill -defined. We are 

 agreed that it must be conceived as a medium which 

 resists strain, but we are not certain how to represent best 

 the relative motions that follow on relative change in the 

 position of the ether-elements. We are not yet satisfied 

 with a perfect fluid, a perfect jelly, or even a turbulent 

 perfect fluid conception of the ether. 



Treating the ether not as a conception but as a 

 phenomenon, we find it difficult to realise how a continu- 

 ous and smne medium could offer any resistance to a 

 sliding motion of its parts, for the continuity and same- 

 ness would involve, after any displacement, everything 

 being the same as before displacement. The idea of a 

 perfect jelly appears to involve some change in structure 

 as we magnify smaller and smaller elements larger and 

 larger. Finally, any relative motion of translation as dis- 

 tinct from one of rotation seems excluded by the idea of 

 absolute incompressibility,^ It is not a metaphysical 

 quibble when we demand that two things shall not occupy 

 the same space, but that when motion begins there shall 

 be somewhere unoccupied for sonietJiing to move into. 

 The obvious fact is that while in conception we can 

 represent the moving parts of the ether as points, and we 

 can endow these points with such relative velocities and 

 accelerations as will best describe our perceptual experience, 

 yet when we project the ether into the phenomenal world 

 it is at once recognised as a conceptual limit unparalleled 

 in perceptual experience, and we do not feel at home with 

 it. The old problems as to " heavy matter " recur. 

 What is the ultimate element of the ether which moves ? 

 and why does it move ? Build a perceptual matter out 

 of a phenomenal ether, and we have again thrust upon us 

 the question as to ether-matter's nature. Is it also to be 

 a terra incognita nunc et in (Eternum ? The mind again 



^ For absolutely incompressible elements (other than points) motion round 

 any closed curve other than a circle seems inconceivable. 



