TO Vermes — Retardation of Alpha Particles hy Metals. 



and clamp so that when in use it can be supported by the ver- 

 ticle rod of the instrument directly above the center of the 

 supports for the foils and the alpha ray source. The micro- 

 scope has a pivot joint near the base, so that it may be swung 

 out of the way when the discharge chamber is ased. The dis- 

 charge point is connected to a string electrometer and a poten- 



FlG. 1 



tial of about 1500 volts is used on the chamber. Polonium 

 which had been deposited on a small copper plate was used as 

 a source of alpha particles. This source was made very strong 

 so there would be a large number of particles even at the end 

 of the range entering the counting chamber. Measurements 

 were made with aluminum, Dutch metal, silver, and gold foils. 

 The results obtained with these foils by the scintillation method 

 appear to be almost identical with those obtained by Marsden 

 and Richardson, and especially in the case of gold and silver, 



