16 THE ROYAL SOCIETY OF CANADA 



of from 50 to 55 volts for the upper gauze was required to remove the 

 glow from the lower gauze. This would correspond to a velocity 

 of approximately 4-2 x 10^ cms. per second for the greatest velocity 

 of any of the secondary rays produced. Apart from this rather high 

 value it will be seen that the behaviour of these rays is in close agree- 

 ment with that of delta rays from metals. 



4. The Direction of Propagation of the Secondary 

 Radiation. It was found that the secondary rays were propagated 

 with greatest intensity along directions making a very small angle 

 with the primary beam. This was easily examined by placing a 

 small screen in such a way that only rays at right angles to the primary 

 beam or from that part which had passed the screen, could enter the 

 testing box, C. If the rays were scattered equally in all directions 

 such a screen should reduce the glow in the box by about fifty per cent, 

 but it was found instead to be almost completely eliminated. Thus 

 the secondary radiation must be mainly in the path and direction of 

 the primary. 



It is intended that the velocity of the radiation should be deter- 

 mined accurately in different gaseous media and over a large range of 

 intensities of the primary beam. Further information concerning 

 their nature, their source of energy, and the critical velocity for pro- 

 ducing luminosity is anticipated. 



The writer is indebted to Professor Sir Joseph Thomson for the 

 suggestion of this research, and desires to express thanks for his kind 

 interest in the preliminary experiments which were performed at the 

 Cavendish Laboratory in the spring of 1913. Many thanks are also 

 due to Professor C. J. Lynde for providing the facilities for continuing 

 the work at Macdonald College. 



Macdonald College, 



McGill University, 

 May, 1915. 



