416 Prof. 0. Lodge on Absolute Velocity and 



is really unchanged. Any other reckoning of the relative 

 energy, such as the usual ^m(v+iv) 2 , where the large mass 

 is considered stationary, is wrong: the error being J(M + ??i)w 2 

 in excess. 



The error, however, is smaller as M is bigger, and vanishes 

 when M is infinite, hence it is usually ignored ; but the error 

 is in principle the same as if the small mass w r ere the one 

 considered at rest, in which case the relative energy would be 

 preposterous. 



Hence velocities cannot rigorously be referred to any 

 artificial standard of rest, but must be referred either to a 

 point which does not move in the particular problem, like 

 the centre of inertia of a system, or to a body which never 

 moves at all, viz. either one of infinite mass or one to which 

 there are no stress attachments. The aether (I proceed to 

 argue), regarded as an omnipresent connecting medium be- 

 tween material bodies, satisfies probably both these conditions, 

 and certainly one of them, and therefore serves as a standard 

 of reference — a universal standard of rest — available in all 

 cases ; in other w r ords, the sether possesses no kinetic energy, 

 at least no kinetic energy accessible through purely mechanical 

 force. 



I next argue that it is the sole medium of stress, i. e. that 

 it possesses all the potential energy there is. And then that 

 all mechanical activity consists in a transference of energy, 

 through the agency of normal force, from aether to matter or 

 vice versa. 



I cannot indeed deny that in some unknown way the aether 

 may be moving progressively as a whole, if such a state- 

 ment has any meaning, which I doubt ; but I maintain that 

 for all practical purposes motion of matter relative to the 

 aether is absolute motion, and is what we really mean by 

 velocity in space, without any appeal to artificial material 

 standards or axes of reference. I am much interested in 

 finding in Dr. Larmor's treatise on iEther and Matter a 

 sentence in some sort of agreement with these views (Phil. 

 Trans. (1897) p. 219). 



First, I state a pair of simple axioms which require no 

 justification, and whose necessary definitions can be easily 

 supplied : — 



1. Stress is Essential to Action. 



2. Stress cannot exist in or across Empty Space. 



(By " free space " I mean space full of aether ; by " empty 

 space " I mean a thing of which we have no experience 

 whatever ; but we have plenty of experience of stress, and 

 cannot conceive its existence except as a modified state of 

 something real.) 



