SECTION A. 





ASTRONOMY. MATHEMATICS, 

 AND PHYSICS. 



ADDRESS BY THE PRESIDENT: 

 Professor H. J. Priestley, M.A., 



Professor of Mathematics in the University of Queensland. 



THE THEORY OF RELATIVITY. 



In opening a discussion at the Royal Society of London, Mr. J. H. 

 Jeans said, " During the last century two great dominating principles 

 of physics emerged, the Conservation of Energy and the Second Law 

 of Thermodynamics. The present cfentury has already added a third 

 member to this list, the Principle of Relativity." 



Whether we are prepared to give the Principle of Relativity such 

 importance or not, the development of that principle is imdoubtedly 

 the most striking advance in Mathematical Physics since the last 

 meeting of this Association. For this reason I propose to devote my 

 address to a survey of the growth of the Theory of Relativity, with 

 special reference to the assurnptions on which it is founded and the 

 experimental evidence from which it draws support. 



The earlier Restricted Theory of Relativity is based on two principles 

 enunciated by Einstein in 1905, namely : — 



I. The Principle of Relativity. 



The laws according to which the states of physical systems 

 are changing are the same, whether they are referred to a 

 co-ordinate system S or to any similar system S' moving 

 uniformly with respect to S. 



II. The Principle of Constant Light Velocity. 



Every light disturbance is propagated, in vacuo, relatively 

 to a system S with a determinate velocity c, no matter whether 

 it is emitted from a source stationary in or moving with respect 

 toS. 



