$2 Sir Oliver Lodge on 



what is practically the same thing, 1 + v 2 /2c 2 ; where c is the 

 characteristic velocity with which every known disturbance 

 is propagated by free sether. It is just this uniformity of 

 transmission which makes the connexion between sether and 

 matter so elusive to experimental observation: measurement 

 is foiled save when matter moves relatively to matter. That 

 is the foundation, and I venture to think all the foundation, 

 for the Theory of Relativity considered as a philosophical 

 reality instead of only a more or less convenient summary of 

 experimental results. 



An increase in inertia, without corresponding increase of 

 gravitational control, cannot fail to have astronomical con- 

 sequences, though they may be so small as to be barely 

 observable. For inertia is a function of speed even when 

 speed is but planetary, and if the force of gravitation is not 

 correspondingly increased — a thing which we have no reason 

 whatever to think likely, since aether is presumably the 

 vehicle of gravitation and not subject to it until contorted 

 into the singular points called electrons, — then some small 

 but cumulative effects may be caused in the more rapidly 

 moving bodies. 



Professor Einstein's genius enabled him in 1915 to 

 deduce astronomical and optical consequences (some not yet 

 verified) from the Principle of Relativity. See an interesting 

 account by Professor Eddington in i Nature/ vol. xcviii. 

 p. 328 (28 Dec. 1916). I wish to show that one of them at 

 least can be deduced without reference to that principle. In 

 so far as the deduction is incompletely in accord with quanti- 

 tative observation, there is something further to be considered ; 

 but it is unlikely that a result of approximately the right 

 order of magnitude can be devoid of significance. 



Consider the amount of the perturbation caused by extra 

 inertia in the case of Mercury, whose orbital speed is approxi- 

 mately half as great again as that of the earth, or say 1*5 X 10~ 4 

 times that of light. In one part of its orbit it will be travelling 

 parallel to and in the same sense as that component of the 

 sun's way which lies in the plane of the planet's orbit, which 

 we may call Mercury's ecliptic. In all this half of the orbit 

 therefore its inertia will be slightly greater than the average 



Historical Note. — Heaviside's expression for the coefficient of ±v 2 in 

 the value of kinetic energy for a charged sphere was first given in 

 Phil. Mag. April 1889* 



J. J. Thomson's expression for the coefficient of v in the value of 

 momentum is contained in his ' Recent Researches in Electricity and 

 Magnetism/ page 21, published in 1893. The above trigonometrical 

 expression is intended to represent this. 



