83 



J^h February, 1921. 



In Physics Lecture Theatre, Queen's University. 

 The President, Professor Gregg Wilson, in the Chair. 



" THE PERCEPTION OF THE INVISIBLE." 



(Illustrated by numerous Experiments). 



By R. T. Beatty, M.A., D.Sc. 



Member of the Soientific Staft of the Admiralty, (by consent). 



{Abstract). 



The lecturer gave a brief review of the methods which men 

 had evolved for transporting themselves and their property over 

 the surface of the earth, and pointed out that while enormous 

 machines had been developed for rapid transport by land, sea, 

 and air, very little provision had been made for preventing 

 disastrous collisions in darkness or fog, for detecting the presence 

 of hostile war machines, or for communicating over distances 

 greater than the eye could reach. 



Even in so recent a period as that of the South African 

 War, the horse and the heliograph (the latter requiring sunny 

 weather for operation) were the only means of communication 

 between rapidly moving troops when some miles apart. In 

 general terms, the great mechanical revolution of the 19th 

 century Avas not accompanied by a corresponding increase in the 

 safety of human life. 



New problems arose in 1914. Communication by wireless 

 in many cases was found to be too public and too easily interfered 

 with. On sea it was often necessary to signal in such a way as 

 not to disclose the presence of the signalling, ship. Methods of 

 detection Avere required : detection of submarines, of approaching 



