Transactions of the Royal Society of Canada 



SECTION III 

 Series III MAY, 1920 Vol. XIV 



PRESIDENTIAL ADDRESS 

 By Dr. A. S. Eve, F.R.S.C. 

 Relativity 

 (Read May Meeting, 1920) 



There is a relativity with which man and animals have been in 

 practice long familiar. A hawk swooping at its prey, a savage shooting 

 an arrow at a moving quarry, a boy striking at a moving ball, make 

 due allowance for relative motion with a precision not less remarkable 

 than that of a gunner on a modern battleship, or a torpedo officer on a 

 submarine, when he allows for the velocity of his swift-moving target 

 relative to his own ship. 



A notable exception is the curve of pursuit of a dog running to his 

 moving master. The dog does not take the quickest path or line of 

 least action, as does a good fielder intercepting a ball at cricket or 

 baseball. The aberration of light, the slanted umbrella, the delusion 

 that your train has started when really an adjacent train has moved, 

 the fact that if you travel with the wind, and at the same pace, to you 

 there is no wind, the relative acceleration in elevators, are all familiar 

 instances of relative motion which have long been appreciated. 



Possibly too in the realms of Philosophy the relativity of our 

 knowledge has been consciously or subconsciously recognized in the 

 search for truth. 



There appears to be a craving in the mind of man for fixed points 

 of reference. In Time this has been achieved, at least apparently, 

 by an event. The Interval between two events has been considered, 

 until recently, a concise and measurable quantity. It is now known 

 to be elusive. The terms "before" and "after" an event are capable 

 of inversion owing to the time required for transference of light signals. 

 Time can be apparently accelerated by rapid approach to a clock, or 

 delayed by recession from it. The moving picture, worked back- 

 wards, familiarizes us with at least a conception of the reversal of tirne. 



The desire for a fixed frame of reference in space has been no less 

 marked. The first conception was a flat and stable earth with heaven 

 above, the "excellent canopy the air, the brave o'erhanging firmament, 



Sec. Ill, Sig. 1 



