Deflexion of u. Particles through Large Angles. 609 



measurements were made simultaneously with different foils. 

 These foils were attached to frames which fitted into a slot 

 in the tube T in such a way that they could be exchanged 

 and accurately replaced in position. Table I. gives an 

 example o£ a particular set of countings, when a silver foil 

 was used to scatter the a particles. 



Table I. — Variation of Scattering with Angle. (Example 

 of a set o£ measurements.) Silver Foil. Time elapsed 

 since filling of emanation tube, 51 hours. Correction 

 for decay, 0*683. 



Angle 



Scintillations per minute. 



1 



JN"Xsin 4 0/2. 



Without 

 foil. 



With 

 foil. 



Corrected 



for effect 



without 



foil. 



Corrected 



for decay, 



N. 



sin 4 <p/'A' 



o 



150... 

 135 .. 

 120... 

 105... 



75... 



60... 



0-2 

 2-6 

 3-8 

 0-6 

 00 

 0-3 



4-95 

 8-3 

 10-3 

 10-6 

 28-6 

 69-2 



4-75 



57 



6-5 



10-0 



28-6 



68-9 



695 

 8-35 

 9-5 

 146 

 41-9 

 101 



1-15 

 1-38 

 1-79 

 2-53 

 7'25 

 16-0 



6-0 

 6-1 

 5-3 



5-8 

 5-8 

 6-3 



In this set about 2500 scintillations were counted. After 

 a few days had elapsed the measurements for the smaller 

 angles were repeated and the range of angles extended. 

 Proceeding in this way the whole range of angles was in- 

 vestigated in the course of a few weeks. When measuring 

 relatively large angles of deflexion a wide beam of about 

 15° radius had to be used in order to obtain a suitable number 

 of scintillations, but for the smaller angles the aperture of 

 the diaphragm confining the beam was reduced considerably, 

 so that the angle at which the scintillations were counted was 

 always large compared with the angular radius of the beam. 

 When changing over from one diaphragm to another com- 

 parative measurements for different angles were made so as 

 to obtain an accurate value o£ the reduction constant. 



Table II. gives the collected results for two series of ex- 

 periments with foils of silver and gold. The thicknesses of 

 the foils were in the first series equivalent to 0*45 and 0*3 

 cm. air, and in the second series 0*45 and 01 cm. air for 

 silver and gold respectively. Col. I. gives the values of the 



Phil. Mag. S. 6. Vol. 25. No. 148. April 1913. 2 T 



