NOTES 45i 



treme difficulty. Mr. Jourdain's use of the classification 

 adopted in the Revue Semestrielle enabled him to give to the 

 expert at a glance the references likely to be useful to him ; 

 and at the same time it allowed him to indicate, by cross- 

 references, what a more " popular " presentation could not 

 have done — namely, the interconnectedness of all branches of 

 mathematics, and the importance (even to technical mathe- 

 maticians) of work on the foundations and development of 

 mathematics. All those who have made use of this part of 

 Mr. Jourdain's work will always owe him a debt of gratitude 

 for its completeness and scholarly accuracy. 



In addition to books on the work of other mathematicians, 

 Mr. Jourdain published The Nature of Mathematics, 191 2 (of 

 which a new and revised edition has just been issued) ; The 

 Principle of Least Action, 191 3 ; and The Philosophy of Mr. 

 B*tr*nd R*ss*ll, 19 19- 



Sir Oliver Lodge and Einstein's Theory (H. S. J.) 



In a lecture to a small but distinguished gathering at Lord Glenconner's 

 residence on November 24 last, Sir Oliver Lodge, after explaining the result 

 obtained from the photographs taken by the recent Eclipse Expeditions, and 

 showing that the observed deflection was twice that which would be anticipated, 

 assuming light to possess inertia and Newton's law of gravitation to be rigidly 

 true, proceeded to put forward some tentative hypotheses to account for the 

 double displacement. Stated very briefly these were : (i) Light is a wave-motion, 

 and the energy is half kinetic and half potential. It might be conceivable, 

 therefore, that a light-wave would have only half the inertia but the whole weight 

 when compared with a material particle. The deflection of a light-ray passing 

 near the sun would then be double that which would be experienced by a material 

 particle moving past the sun with the velocity of light, (ii) In a material body, 

 the velocity of light is modified by interaction between the body and the aether. 

 It is conceivable that the body may even modify the aether in some way for a 

 certain distance outside it. Its specific inductive capacity, and hence its refractive 

 index, would then be modified. This gravitational "aura" may only become 

 appreciable outside a large mass, such as the sun. The deflection would then be 

 a refraction effect, (iii) The deflection obtained from a distance r from the sun's 

 centre may be put in the form 27//C 2 , where v is the velocity in falling from infinity 

 to the point r under the sun's gravitational field and c is the velocity of light. 

 Light starts from infinity with velocity c, which cannot be increased. Gravitation 

 is striving to increase the longitudinal energy, but is unable to do so. If it is 

 supposed that by a sort of gyrostatic effect the additional energy %mv 7 is added in 

 the transverse direction instead, it can easily be shown that the observed de- 

 flection is obtained. 



Sir Oliver Lodge then proceeded to deal with some of the bearings of Einstein's 

 theory, and explained how it revolutionised our conceptions of space and time. 



Prof. Schuster, in proposing a vote of thanks, said that, as a student of the 

 history of science, he thought that the safest way to deal with the new theory was 

 not to seek for alternative explanations, but to adopt it and follow it to its logical 



