866 Dr. Kovarik and Mr. Wilson on the Reflexion of 



coefficients of absorption by aluminium lie between 75 and 

 about 20 (cms.) -1 it is greater for the rays of greater 

 velocity ; for the very penetrating rays the percentage 

 decreases again. 



(6) The percentage of reflected /8-particles is greater for 

 the reflectors of greater atomic weight. 



(7) By multiple reflexion the ionization may be increased 

 from 100 to 350. The multiple reflexion changes in value 

 with the atomic weight of the reflector, and the velocity of 

 the /3-particles in the same manner as the single reflexion. 



These experiments were suggested by Professor Rutherford, 

 to whom I wish to express my deep gratitude for his valuable 

 suggestions, attention, and the permission to work in his 

 laboratory. 



Physical Laboratory, 

 Victoria University of Manchester. 

 July 4, 1910. 



\('IV. On tin' Reflexion of Homogeneous ^-Particles of 

 Different Velocities, By Alois F. Kovarik, Ph.D., 

 and \Y. Wilson, M.Sc* 



IN the preceding paper by one of us it was shown that the 

 ratio of the number of /3-particles reflected from a sheet 

 of matter to the Dumber impinging upon it increased, within 

 certain Limits, with the penetrating power of the rays. This 

 result was found for the heterogeneous rays emitted by 

 radioactive bodies. The following experiments were made 

 to determine the variation of this ratio for approximately 

 homogeneous rays of different velocities. Such rays were 

 sorted out by means of a magnetic field. 



The apparatus used is shown in fig. 1. The rays were 

 emitted by the active deposit in equilibrium with radium 

 emanation, corresponding to about 30 mmg. of radium, con- 

 tained in the bulb A. They entered the magnetic field B 

 and described circular paths passing through the hole R 

 and the tube S into an ionization vessel. The ionization 

 vessel consisted of three parallel leaves of thin aluminium 

 foil on rigid frames, 10 cms. x 10 cms.; the outer two metal- 

 lically connected together were about one centimetre apart ; 

 the inner one was separated from the outer two by means of 

 sulphur, and it was connected by a protected wire to the 

 gold-leaf system of a small electroscope E by means of which 

 the ionization in the vessel was measured. The tube S was 



* Communicated by Prof. E. Kutherford, F.E.S. 



