1254 



sensitive mbljbdeiiite-piatinum detector EJ, the straight part in the 

 tirst quadrant is very prominent. This part was obtained by sending 

 the current from the crystal to the point and was measured before 

 the electrolysis had become perceptible. Evidently the cui-ve may be 



E-e 

 represented again by the formula 7 = — ït^' ^^ which R is the con- 

 stant real resistance and e a hypothetical counter E. M. V. That tlie 

 real resistance is i-epresented by the slope of the straight part appears 

 when a series of very brief current impulses is sent through the 

 contact. We then find successively the characteristics ^i 11 and £", IK, 

 which in the tirst as well as' in the third quadrant approach more 

 and more to a straight line through the origin parallel to the straight 

 part of the other charactei-istics. This will still be clearer when we 

 consider the characteristics of a number of other detectors. 



In this case also we may assume the existence of a counter 

 E. M. F'. with a maximum of about 1.1 Volts, though the latter could 

 not be detected with the Wuli'' electrometer. For, if the current is 

 passed for some time longer, so that the electrolysis becomes clearly 

 visible with the microscope, the characteristic of the contact changes 

 froiji E^ 111 to E, IV. If further the contact pressure is diminished, 

 curve E^ V will be obtained showing again clearly the unidirectional 

 resistance. If finally this crystal, after some further electrolysis, is 

 connected with the Wulf electrometer a polarisator E.M.F. of 1.1 Volts 

 will be measured. During this gradual transition of the characteristic 

 E^ I into E^ IV the real resistance remains constant and this proves 

 that the unidirectional resistance of the contact even without any 

 electrolysis being visible, must be attributed to an electrolytic counter 

 E. M. F. in an extremely thin film. 



With strong currents the straight part becomes curved, the concave 

 side being towards the vertical axis. In the 3'<* quadrant no straight 

 part can be obtained at all. This is due to the decrease of the real 

 resistance of similar substances^) with rise of temperature. With 

 molybdenite the conductivity is doubled already with rise of tempe- 

 rature from — 200° C. *). It appears from the quick evaporation 

 of a drop of oil placed on the point of contact that this rise in 

 temperature caused by a current of 0.03 Amp. is considerable. 



Carborundum-steel. With the very sensitive carborundum-steel 

 detector no phenomena of electrolysis could be seen. Nor was it 

 possible, except by applying a strong E.M.F. to change the charac- 



1) 0. Reichenheim, Ueber die Elektrizitatsleitung einiger natiirlich kristallisierten 

 Oxyde und Sulfide und des (baphits. In angural Dissertation, Freiburg 1906. 

 3) A. E. Flowers, Phys Review 1st. Ser., Vol. XVIII, 1909. 



