THE DISCOVERY OF ELECTRON WAVES 



479 



Oazimuth 



Fig. 1 — Schematic diagram showing disposition of primary beam, nickel crystal 

 and collector. Crystal shown revolved to bring one principal azimuth after another 

 into plane of observation. 



neighbors, could be moved on an arc about the crystal. The crystal 

 itself could be revolved about the axis of the incident beam. It was 

 possible thus to measure the intensity of elastic scattering in any 

 direction in front of the crystal face with the exception of those direc- 

 tions lying within 10 or 15 degrees of the primary beam. 



54 V. 



64 V 



68 V. 



Fig. 2 — Polar diagram showing intensity of elastic scattering in A-azimuth (see Fig. 1) 

 as function of latitude angle, for series of primary beam voltages. 



The curves reproduced in Fig. 2 show the distribution-in-angle of 

 intensity for a particular azimuth of the crystal. The curves are for a 

 series of electron speeds, therefore, for a series of electron wave-lengths. 

 For a particular wave-length a diffraction beam shines out. Setting 

 the collector on this beam at its brightest and revolving the crystal, 

 the intensity was found to vary in azimuth as illustrated in Fig. 3. 



