of a-F articles per Second emitted by Thorium C. 1039 



and a-particles of range 6*96 cm. and 3*8 cm., the latter, 

 however, appearing in negligible numbers. In this experi- 

 ment the a-particles counted were those of S'6 cm. and 

 6*96 cm. range. 



The deposit of thorium C was obtained in the usual way 

 by rotating a nickel disk for about half-an-hour in a solution 

 of radio-thorium. To obtain radium a quantity of emana- 

 tion was allowed to decay overnight, compressed in a small 

 glass tube. The active deposit on the walls of the tube was 



Fig-, l. 



G/ass Tube. 



\Centr/ng Piece. 



7=\~ 



Source. 

 Omms, 



Af/ca = — » 

 ■f-3 cms-Air. 



M/'croscope 

 06/hci/Ve. 



q- PARTICLE 



oourmriG apparatus . 



¥ 



Bear/n<?s of Cot/rtt/ng V//?ee/. 



X 



IA 



G/ass W/?ee/ 



rs/th 

 Brass Stit. 



then dissolved in 10 per cent, hydrochloric acid, and the radium 

 C obtained by stirring the solution for about three minutes 

 with the nickel disk. The disk used was of 8 mm. diameter, 

 and was carefully protected by sealing-wax on the back and 

 edges while depositing the active material. Check experi- 

 ments on the back of the source showed that an inappreciable 

 number of a-particles was emitted from it. 



The experimental arrangement for counting is shown in 

 the accompanying diagram (fig. 1). The nickel source was 



