708 



Mr. A. B. Wood on the Velocities of the 



1*922 x 10 9 cm. /sec. as the velocity of the a-particles from 

 radium C. For this purpose it is necessary to analyse the 

 a-particles emitted from thorium active deposit and from 

 radium C under identical conditions. This was accomplished 

 by introducing- a slight modification into the experimental 

 procedure outlined in the previous section. 



The platinum wire, after a long exposure to thorium ema- 

 nation, was introduced for about 15 minutes into a small 

 chamber containing a few millicuries of radium emanation*. 

 After an interval of 20 minutes, when the radium A on the 

 wire had practically disappeared, the wire, now coated with 

 thorium active deposit and radium C, was introduced as 

 before into the deflexion apparatus. Henceforward the ex- 

 perimental procedure was the same as in previous experi- 

 ments. On developing the plate one observed, instead of 

 two lines only in the deflected positions, three lines — the 

 third, intermediate, line being obviously due to the a-particles 

 from the radium C. The best photographs were obtained in 

 the experiments where the magnetic field was not reversed. 



Fig. 5, PL XVII. shows the appearance of a plate obtained 

 in such an experiment. In the deflected position 3 lines are 

 shown, the outermost line being due to the a-particles of 

 range 4*8 cm. (from thorium Ci), the intermediate line to 

 a-particles of range 6*94 cm. (from radium C), and the 

 innermost line due to a-particles of range S'6 cm. (from 

 thorium C 2 ). Table II. gives a few of the accurate measure- 

 ments made on plates of this character — the deflexions cor- 

 responding to a magnetic field in one direction only, 

 measurements being made from the central undeflected 

 line. 



1 = 4,-0 cm. 



Table II. 

 H varies between 9,000 and 10,000 gauss. 





d r . 



Deflexion in cm. 



of a-particles 



from Thorium 2 . 



d r 



Deflexion in 



cm. of particles 



from Eadium C. 



d 3 . 



Deflexion in 



cm. of particles 



from 



Thorium C r 



.Ratio of radii of 

 curvature of 

 paths. 



Pi '• P 2 '• Pa- 



1... 



2... 

 3,.. 



0*4085 

 0-4070 

 0-3914 



0-4385 

 0-4380 

 0-4210 



04935 

 0-4921 

 0-4720 



1 : 0-934 : 0832 

 1 : 0-932 : 0-831 

 1 : 0-932 : 0-831 



p u p 2 , and p 3 are calculated as in Section I. 



* Supplied to me through the kindness of Sir E. Rutherford. 



