A TEST FOR ELECTRON POLARIZATION 



469 



than any other because our earher observations on electron reflection 

 were made with the incident beam in this azimuth, and several of the 

 critical electron speeds for 45 degrees incidence were already known. 



Each reflector is attached to a triangular frame which is supported 

 from the diagonal wall of the enclosure through three adjusting screws. 

 Two only of each set are shown in Fig. 1. The frames to which the 

 crystals are attached and other accessory parts have been omitted from 

 the drawing in the interest of clearness. 



Small tungsten filaments, mounted one behind each of the reflectors, 

 are supported by stifle wires from quartz plates which are clamped to 

 the outer walls of the enclosures. Electrons emitted by these filaments 



Fig. 2 — Schematic diagram illustrating the principle of the experiment. 



are used for heating the reflectors by bombardment. The reflectors are 

 not insulated from the enclosures, which in fact contain no insulating 

 material whatever except that incorporated in the gun and the collector. 

 The metal parts of the collector comprise an inner and an outer box 

 of circular cross-sections and a cylindrical guard electrode of inter- 

 mediate diameter. These parts are separated by cylinders of pyrex 

 glass, and the assembly constitutes a unit which fits into the end of the 

 collector enclosure. The aperture in the outer box is circular and 2 

 mm. in diameter; that in the inner box is of the same form but of 

 slightly greater diameter. The guard cylinder is interposed to inter- 

 cept the leakage current which would flow otherwise from the outer to 

 the inner box. It was anticipated that the electron current entering 



