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LXXVII. Connexion between Light and Gravitation. 

 By Sir Oliver J. Lodge *. 



EINSTEIN'S great achievement is to begin the association 

 of Gravitation with the electro-magnetic phenomenon 

 called Light, as it has long been associated with the other 

 presumably electrical phenomenon called Matter. The inertia 

 of Matter is affected by motion, and in the case of Light 

 seems to be generated by motion. Assuming that the mass 

 of Light is proportional to its kinetic energy, while the weight 

 of Light is proportional to its whole energy, Einstein's result 

 obviously follows. (Phil. Mag., August 1917, page 93.) 



Another mode of regarding the result would attribute to 

 the mere neighbourhood of Matter a small influence on the 

 specific inductive capacity of otherwise free space, analogous 

 to the influence familiarly exerted in its interior, In other 

 words, to extend to a gravitational field a trace of the effect 

 known in a cohesional field ; a sort of loading of the 

 iEfcher by Matter at a distance. A spherical field whose re- 

 f ractivity was proportional to the gravitational potential would 

 then bend a ray in accordance with x/llcIs stationary, and 

 would give a deflexion inversely as the shortest distance 

 between ray and centre of attraction, as fact requires. The 

 /* — 1 required at each point to give the observed deflexion, 

 quantitatively, is the ratio between the energy of free fall 

 from infinity and the energy of motion with the velocity of 

 light. 



The former method seems the simpler, but both require a 

 detailed theory of weight beyond what has yet been attained. 

 A particle falling towards the sun would be accelerated 

 longitudinally and also deflected transversely. Light cannot 

 be accelerated longitudinally: all the accelerative effect of 

 gravity must go (gyrostatically) into transverse deflexion. 

 Consequently when it has reached the shortest distance all the 

 deflexion to be expected from weight has been produced. The 

 other half deflexion is generated during recession. 



* Communicated bv the Author. 



