MOTION THROUGH ETHER 243 



think will soon be superseded, when the fashion has passed. 

 It may be even regarded as comparable in utility to the 

 second law of thermodynamics, which has been used by philo- 

 sophers and theologians, with doubtful security, to justify 

 conclusions in eschatology. But if technical theorems or 

 handy formulae are employed to confuse elementary ideas, to 

 deny straightforward dynamical conceptions, and to justify 

 the deduction of portentous consequences about space and 

 time, so as to complicate not merely details of measurement 

 but the whole of our physical conceptions, then it is time to 

 protest. 



The postulate that axes of reference can be shifted and 

 chosen arbitrarily without making any real difference to 

 phenomena is a perfectly reasonable one, and in Einstein's 

 hands, in combination with the fundamental FitzGerald- 

 Lorentz factor ( 1 — v 2 /c 2 ) representing the connection between 

 matter and ether, has enabled certain deductions to be simply 

 made. 



Whether a body moves through stationary ether, or 

 whether ether streams past a stationary body, makes no 

 difference. Granted that, and granted also that light travels 

 at a constant speed through free ether, and we have all that 

 is needed for the original Einstein deductions ; which really 

 depend for their interest not on the assumption of trivial 

 axioms but on the ingenious employment, throughout, of the 

 above factor. Recently we have learnt that he has pushed 

 the liberty of choosing co-ordinates further, and by endowing 

 his standard with acceleration, say the acceleration due to 

 gravity at any particular place, and again by consistently 

 using the Lorentz factor for all moving matter, he appears to 

 have made astronomical deductions of interest and importance. 

 For by this means gravitational influence can be made to 

 disappear from a specification of motion, and an accelerated 

 body can move with reference to a suitably accelerated 

 standard as if under no force. 



All honour to the ingenuity of the conclusions thus deduced, 

 in so far as they are confirmed by observation ; but let us not 

 stultify ourselves by thinking that the body is really subject 

 to no force, and freed from acceleration, because of some 

 mathematical artifice adapted to co-variant or relativist treat- 

 ment. Use a falling stone, or a cloud of falling stones, as the 



