Deflexion of a. Particles through Large Angles. 607 



the scattering foil F, and a microscope M to which the zinc- 

 sulphide screen S was rigidly attached. The box was fastened 

 down to a graduated circular platform A, which could be 

 rotated by means of a conical airtight joint C. By rotating 

 the platform the box and microscope moved with it, whilst 

 the scattering foil and radiating source remained in position ,. 

 being attached to the tube T, which was fastened to the 

 standard L. The box B was closed by the ground-glass- 

 plate P, and could be exhausted through the tube T. 



Tm. 1. 



The source of a particles employed was similar to that 

 used originally by Rutherford and Royds * in their experi- 

 ments on the nature of the u particle. It consisted of a 

 small thin-walled glass tube about 1 mm. in diameter, con- 

 taining a large quantity of well purified radium emanation. 

 The a particles emitted by the emanation and its active 

 deposit could pass through the glass walls without much re- 

 duction of range. For these experiments the unhomogeneitv 

 of the source, due to the different a particles from the emana- 

 tion, Ra A and Ra C, does not interfere with the application 

 of the law of scattering with angle as deduced from the 

 theory, as each group of « particles is scattered according to 

 the same law. 



By means of a diaphragm placed at J), a pencil of a par- 

 ticles was directed normally on to the scattering foil F. By 



* E. Rutherford and T. Royds, Phil. Mag. vol. xvii. p. 281 (1909). 



