4 THE ROYAL SOCIETY OF CANADA 



As to the properties of space, there is to-day a great confusion of 

 mind. There are those, who like Planck, stoutly maintain that "the 

 sether is a superfluous hypothesis, and should be abolished." Larmor 

 considers such an idea "repugnant to commonsense." 



Space must be a plenum or a void. Electromagnet phenomena, 

 wireless, radiant heat, light, X and gamma rays have an immense range 

 of frequency and of intensity, but their velocities are alike c, and 

 they are waves, capable certainly of interference. 



The light from a star may spread outward on a sphere of as much 

 as 2,000 light years' radius. It is useless to think of quanta or bundles 

 of energy in such cases. Hence we are tied to an undulatory theory, 

 and a void can scarcely be expected to undulate. Indeed the proper- 

 ties of space are those set forth in Maxwell's Electro-magnetic Equa- 

 tions. Can a space warp ? Can it be Euclidean or non-Euclidean ? 

 These concepts originate and end in the human mind. The resulting 

 ideas can be checked by experience and observation. The mechanical 

 aether is dead; an electromagnetic sether is permitted, but not 

 "explained." Perhaps it is crude thinking which makes us prefer to 

 have undulations in a medium entirely unrealized, than to have 

 undulations completely mysterious in a void. 



Once again mathematical reasoning starting from experience has 

 carried us forward into regions, faithfully portrayed by mathematical 

 symbols, whose physical characters are beyond our powers of thought. 

 So Maxwell preconceived wireless waves, Planck found his fundamental 

 constant h, and now Einstein brings us into a strained space wherein 

 not only does light bend, but the sun holds its planets in their orbits. 



There is one point in the principle of relativity to which perhaps 

 sufficient attention has not been directed. Faraday appears to have 

 thought of lines and tubes of magnetic and of electrostatic force or 

 induction as having physical reality. The views of Sir Joseph Thom- 

 son has emphasized such conceptions. Must we not now consider 

 them as conceptions with no physical reality ? 



An electron travelling past you is an element of current, carrying 

 with it a magnetic field. Travel, however, with the electron and to 

 you there is no magnetic field. 



A charged sphere shot past you has magnetic lines around it. 

 Now keep the sphere "stationary" and go past it with reversal of 

 relative velocity, and that sphere has to you a magnetic field around it. 



Indeed if I go past it swiftly in one direction and you pass it 

 swiftly in the other, then the magnetic lines are to us two in opposite 

 directions. They are relative phenomena, so that the generation of 

 magnetic lines by moving charges has no absolute significance nor can 

 the line be said to have absolute value or existence in space or aether. 



