338 



Mr Wellisch, An Electric Detector 



found impossible to record the conditions present when a high 

 degree of sensitiveness had been obtained, so that it was a matter 

 of difficulty to reproduce these conditions ad libitum. However, 

 as a rough example of one set of conditions, it was found that with 

 the air at a pressure of '76 mm., and with one electrode connected 

 to the negative pole of a battery of 400 volts, the tube would 

 respond to faint electric impulses provided the capacity, resistance, 

 and self-induction were suitably adjusted ; the electrometer needle, 

 otherwise stationary, would be deflected on the arrival of the wave. 

 The object of the high resistance R was to cause the needle to 

 return quickly to its zero so that any succeeding impulse might be 

 readily detected. 



i^ 



m 



Hh 



m. 



^ 

 •M?^' 



HlUllULLm- 



L 



r^i^/4 



II-- 



B 



II- 



The effect of an extraneous electric impulse is probably to set 

 up electric oscillations in the circuit including the vacuum tube ; 

 the electric force in these oscillations, when superposed on the 

 electric field in the tube, may then suffice to produce a discharge 

 in the gas. It is important to notice that this discharge need not 

 be, and in most of the cases investigated was not, luminous ; its 

 occurrence is manifested merely by the galvanometer or electro- 

 meter deflection. In this respect the present detector differs from 

 Zehnder's Trigger Tube* in which the induced electric oscillations 

 precipitate an electric discharge from an auxiliary battery and thus 

 produce a glow in the tube. Another method for detecting electric 

 waves which depends upon the same principle is that due to 

 Boltzmann '\, In this method a battery is on the verge of charging 



* Wied. Ann. Vol. xlvii. 1892, p. 77. 

 t Wied. Ann. Vol. xl. 1890, p. 399. 



