18 president's address — SECTION A. 



criticism of Einstein's position with the following remark : — " The 

 fact is that anything that could exist could in theory be perceived 

 if we had the right kind of senses, and the question whether our senses 

 would need much or little modification in order to perceive a suggested 

 entity has not the least bearing on the question whether that entity 

 exists and can be taken as a vera causa." He concludes that no weight 

 can be laid on Einstein's argument to prove that the explanation of 

 rotational effects must be found in a relationship to other parts of the 

 material world. 



Broad himself suggests that rotational effects might be due to rotation 

 relatively to the aether. It should be remembered that it is not correct 

 to say that the Principle of Relativity excludes the possibility of an aether. 

 The old conception is certainly excluded, but Cunningham has worked 

 out a conception of the aether which fits into the scheme of the older 

 Special Theory of Relativity, while Larmor and Eddington both 

 contemplate the possibility of an aether under the General Principle. 

 Broad's suggestion is therefore worthy of attention, but it is doubtful 

 whether the difference between his aether and Einstein's unperceived 

 world matter is much more than a question of words. 



All of these attempts to evolve a theory of the inertial frame are in- 

 teresting, and, to a certain extent, successful, but none of them are 

 wholly satisfactory. They must, for the present, be considered as 

 speculations as to possible solutions of the problem. 



In my opinion the Theory of Relativity is based on sound foundations, 

 is well supported by the results of observation, and constitutes a very 

 real and important advance in theoretical physics. On the other hand, 

 it is far from complete and leaves many problems unsolved, the question 

 of the inertial frame being one, and an important one, of these. 



The Newtonian scheme is such a close approximation to the more 

 accurate Dynamics of Einstein, and it is so much easier to work with, 

 that it is likely to maintain its old position as the basis of work in 

 which we are not concerned with velocities comparable with the velocity 

 of light. The older Mathematical Physics founded on the Geometry 

 of Euclid and the Dynamics of Newton has still much important work 

 to do, and I should like, in conclusion, to ask you, and especially the 

 younger men among you, not to allow the fascination of a new idea 

 to induce you to neglect work which badly needs doing. 



