248 



THE ROYAL SOCIETY OF CANADA 



face A, no matter which terminal of the battery was earthed. Re- 

 peated tests confirmed this conclusion. The same characteristic held 

 for diamond No. 2. 



The dark current became greater with time of application of the 

 field, and on higher voltages there was also a small current from face 

 A to face B. The growth of current with time in diamond No. 1 is 

 illustrated in Fig. 7, which shows no saturation, but continues to 

 grow. Fig. 8 illustrates the growth of current with time in diamond 

 No. 2, and shows that the current reached a saturated state. This 

 curve also shows that the current was unstable, and did not reach 

 a state of equilibrium. 



The variation of dark current with voltage is seen in Fig. 9 for 

 diamond No. 1, and Fig. 10 for diamond No. 2. For these curves, 

 deflection attained in 10 seconds was taken as a measure of the 

 dark current. The numbers on the curves in Fig. 9 refer to the positions 

 illustrated in Fig. 6. The law established by Streintz and Wessely^ 



-4n5 



ArxB 



rl 



^-, fl^. .. 



/V<? CURREtiT 



LARGE CURBENT 



m 



LARGE CURRENT 



NO CURRENT 



Fig. 6 



for lead glance and iron pyrites crystals, that the unipolarity U, 

 defined as Z7 = — "-, is proportional to applied voltage, did not 



hold for the diamonds. In the above formula, lit is the current 

 in one direction, and /21 in the opposite direction. 



The influence on the magnitude of the dark current of the direc- 

 tion in which it flows through the crystal was borne out in the number 

 of tests. Diamond No. 1 was tried with both long and short ends 

 pressed against the electrodes, and in both cases it was found that 

 the large, dark current resulted when the current flowed in a definite 

 direction through the crystal. Consistent results were obtained when 

 both electrodes were pressed on face A, and on face B, of the crystal. 

 While the ratios between dark currents in opposite directions varied 

 greatly with change of position of the electrodes, the direction of 

 maximum dark current in the crystal was preserved throughout. 

 ^Streintz and Wessely, Phys. Zeitschr. 21, pp. 42-50, Jan. 15, 1920. 



