368 Taylor — Retardation of Alpha Bays by Metals. 



with a planimeter. it was found they were equal. This con- 

 firms the observations by Bragg* that the total ionization pro- 

 duced by the alpha particle in air is the same as that in hydro- 

 gen. From the curves of figure 2 it is seen that when the 

 speed of the a-particle is high more ions are produced per 

 centimeter of path in air than in hydrogen, but when the 

 speed is low more ions are produced per centimeter in hydro- 

 gen than in air. 



Fig. 2. 



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Fig. 2. The ordinates of the curves are the distances in centimeters of 

 the polonium from the ionization chamber. The abscissas are the deflec- 

 tions in centimeters of the electrometer needle per second. Curve I was 

 obtained in air at a reduced pressure of about 17 centimeters of mercury. 

 Curve II was obtained in hydrogen at normal pressure. 



*Phil. Mag., March, 1907, p. 333. 



