246 THE ROYAL SOCIETY OF CANADA 



Photo-electric Properties of Diamond No. 2. 



Diamond No. 2 differed from Diamond No. 1 in that it showed 

 a high photo-electric sensitivity in fields as small as 40 volts per cm. 

 Like diamond No. 1, the unilluminated crystal was conducting in 

 one direction only, and comparatively large currents could be ob- 

 tained through it on the application of very small potentials. 



Readings of the photo-electric sensitivity were made in a field 

 of 80 volts per cm. At this voltage the dark current was so large 

 that the image moved off the scale, but a fairly steady zero was 

 maintained by means of a bar magnet, adjusted so as to keep the 

 spot of light at the desired position on the scale. The difficulty 

 mentioned in connection with diamond No. 1, of great unsteadiness 

 in the photo-electric current, was not encountered with the potential 

 used, but became serious as the voltage increased. 



Fig. 4 gives a number of curves showing the rise and decay of 

 photo-electric current with time. It is of interest to note that the 

 current continued to flow a short time after the light was shut off, 

 when the time of exposure to light was not sufficient for the current 

 to reach a maximum. As in crystal No. 1, the lag in decay of the 

 current was considerably greater than the lag in growth. 



Fig. 5 shows the variation of photo-electric sensitivity of diamond 

 No. 2 with wave-length of exciting light. It is very similar to that 

 obtained for diamond No. 1. The deviation from a smooth curve is 

 present, and the rise in sensitivity in ultra-violet light is also evident. 

 The maximum sensitivity occurs at X = 2894 A. 



Properties of Kunzite and Willemite. 



Crystals of kunzite and willemite were absolutely non-conduct- 

 ing when unilluminated. On exposure to light they showed no 

 trace of being photo-sensitive either at room temperature or when 

 cooled to -15°C. 



Undirectional Conductivity. 



As has been mentioned, diamonds No. 1 and No. 2 showed uni- 

 directional conductivity. On investigation, it was found that the 

 magnitude of the current obtained through the unilluminated crystal 

 was governed by the direction of the current through the crystal. 

 This result is illustrated in the diagrams in Fig. 6. For this work, 

 diamond No. 1 was used. The change in direction of the current 

 between positions I and II was made by means of a reversing switch. 



From these figures, it is seen that the dark current flowed only 

 when the direction of the current in the crystal was from face B to 



