PHYSICAL SCIENCE.

Dominion, Volume 6, Issue 1832, 19 August 1913, Page 5

PHYSICAL SCIENCE.

"THEORY OF RELATIVITY," By Telegraph—Press A63ociation—Copyright London, August 17. Sir Oliver Lodge's presidential addiross to the British Association will combat the new schools of physicists, who 1 dispute tihe universality of ether in favour of the theory of relativity. The uniform failure of all attempts to disoover "absolute" .motion through the aether even under the promising conditions of the olassical experiment of Mictoelson and Morl6y, was met in the first instance by FitzGerald and Lorentz's hypothesis of a shrinkage of all matter in the direction of such motion. Such an-hypothesis, though not unreasonable, was entirely arbitrary, and open to the objection that the amount of shrinkage should depend in some way upon the substance in question. .

A more radical solution was furnished in 1905 by Dr. Albert Einstein, of Bern, now Professor' of Theoretical Physics in the German University of Prague. This solution is based' on the "Principle <of Relativity," a principle which extends to electromagnetic phenomena that inde--pendenoe of absolute motion wliich has bien accepted for mechanical 'systems since the days of Newton. It makes tiro fundamental assumptions, which may bo put concisely as follows: (1)_ It is impossible to disoover absolute motion by means of electromagnetic (including optical) phenomena; (2) the velocity of light is a universal constant, independent of the motion of the source.'

Once we admit the materiality of radiant energy, we are obliged to consider tho question of it being subject to gravitational force. Einstein, indeed, goes so far as to answer the question in the affirmative, and boldljr predicts Hie observation of the gravitational deflection of a beam of light from a star by tho sun's gravitational field, a deflection which, though only amounting to 0.83 degrees, ought to be unmistakable. however, the relativity theory is on dangerous ground, for any suoh gravitational effect on beams of light contradicts _ its own second fundamental assumption, whioh-postulates the absolute constancy of the velocity of light. _ This absolute constancy is ail that remains of tho properties of the luminiferous aether, which adherents of the relatively theory sometimes profess to have completely eliminated. As it stands, it' really represents a modus vivendi by means of which tho substance of tho' undulatory theory and the aether principle may be saved in spite of .the overwhelming negative evidence which has accumulated against the latter. Should this _ attempt fail, there is alwn.vs the alternative of assuming that the velocity of light is added to that of the source, as it is in thie electromagnetic theory devised by Bitz. This, of course, means the total abandonment of the aether as a luminiferons medium, and the revival of the emission theory of light.