A TEST FOR ELECTRON POLARIZATION 471 



to insure the desired orientation of the crystal with respect to the 

 incident beam. Short wires attached to the reflector and protruding 

 from it were rested upon the frame, and the reflector was then turned 

 until the triangles on its surface stood in opposition to the triangle 

 formed by the frame, this being the necessary relation. This adjust- 

 ment was made with the frame and reflector mounted on the movable 

 stage of a tool maker's microscope. One of the wires was then elec- 

 trically welded to the frame. The adjustment was disturbed slightly 

 by this operation, but the disturbance was corrected for by bending 

 slightly the attached wire before proceeding with the second weld. 

 This alternation of adjustment and welding was continued until all 

 wires were attached. As finally adjusted the orientation of the 

 reflector may have been wrong by one or two degrees, but hardly by 

 more. 



In adjusting the first reflector for position two conditions sought 

 were, first that the intersection of the axis of the gun with the axis of 

 the movable system should lie in the surface of the reflector, and second 

 that the normal to the reflector should bisect the angle formed by these 

 axes. These were attained by removing the collector enclosure from 

 the frame of the apparatus and the filament from the gun, and coUimat- 

 ing the collector enclosure bearings with the images of the gun apertures 

 formed by the reflector. For making the similar adjustment of the 

 second reflector an aperture was formed in the center of the rear wall of 

 the collector so that a view of the reflector might be had along the 

 collector axis. The gun enclosure which had been detached from the 

 frame of the apparatus during the adjustment of the second reflector 

 was then replaced, and the adjustment of the two reflectors was checked 

 by directing a beam of light along the axis of the gun and finding that 

 the twice reflected beam proceeded accurately along the axis of the 

 collector. 



The preparation of the tube — the preheating of the metal parts, the 

 baking, the exhausting, and the sealing off — was the same essentially 

 as described in an earlier paper to which the reader is referred for 

 particulars. (Phys. Rev., loc. cit.) 



In operation, the tube is mounted in a cradle with its axis inclined 

 30 degrees from the horizontal, so that an auxiliary tube lying in the 

 axis and containing charcoal may be kept submerged in liquid air. 

 The movable system swings to the lowest part of its arc, and its angular 

 position with respect to the frame of the apparatus is read against the 

 circular scale shown in Fig. 3. To alter this azimuth angle 6 the tube 

 is rotated about its axis; actually the "movable system" remains at 

 rest relative to the earth, and all other parts are rotated. 



