Conclusions of tJie Theory of Relativity. 851 



If we accept Einstein's postulates, nothing is more beau- 

 tifully logical than his conclusions. If it is the function of 

 mechanics first to explain radiation and electrodynamics 

 rather than the motion of ponderable bodies, then it may be 

 wise to modify all those things which seem most real to us 

 to make them harmonize with the properties of that creation 

 of our imagination,, the electron. Let us by all means create 

 an electron subservient to the Lorentz-FitzGrerald trans- 

 formation and subject to all the consequences which that 

 subserviency involves. We shall have a model which we 

 can fashion so as to explain the Michelson-Morley expe- 

 riment, the bending of light rays and many other puzzling 

 phenomena ; we can even assume Langmuir's atom which 

 supposes matter to be nothing but electrons which are con- 

 fined in cells whose stuff is hypergeometric. If the remarkable 

 discovery of the bending of light by the sun is confirmed we 

 are, almost certainly, going back to a corpuscular theory of 

 light, whose particles will have a real gravitational inertia. 

 But when we have arranged a myriad or so of these com- 

 placent electrons into a bit of uncompliant real matter, then 

 we should go back to our classical mechanics with its in- 

 variable inertia and its other laws. 



Out of the theory of relativity, there has come one problem 

 of a purely mechanical nature. It is a distinct achievement 

 that Einstein has found an additional term to Nekton's law 

 of gravitation which accounts for the motion of the perihelion 

 of Mercury. It is undoubtedly a very remarkable fact that 

 it should have resulted as a deduction from Einstein's pos- 

 tulates. There is, however, no reason why a second term in 

 the law of gravitation should not be found from purely 

 mechanical postulates, and there are many indications that 

 we shall sooner or later find the dependence of gravitation on 

 temperature, time, the medium, &c. The recent paper by 

 Sir George Grreenhill in this journal discusses the problem 

 of Mercury; the additional term of Einstein is reduced to 

 ordinary O.G-.S. units, and if he is correct in his deduction: 

 " Einstein's m must denote a length, in centimetres. It is 

 mysterious then that Einstein is quoted as calling m the mass 

 of the Sun, as if amass could be measured in centimetres, by 

 a metre rule, and not in grammes ; some mysterious unex- 

 plained astronomical units must have been employed, and 

 writers should enlighten us on this point of the theory." This 

 is really not more mysterious than many other things in 

 physics. If we explain a quantity of electricity as a complex 

 unit of mass, length, and time without objection, should we 



