PIERCE. — CRYSTAL RECTIFIERS FOR ELECTRIC CURRENTS. 331 



consists of a nearly sinusoidal curve for one half period and a practi- 

 cally straight line for the other half period. The large current flows 

 from the copper to the molybdenite, and the zero current from the mo- 

 lybdenite to the copper. 



When the pressure on the contact was increased until a small nega- 

 tive current was permitted to pass, oscillogram No. 2 was obtained. 

 Increasing the pressure still more so as to get a larger negative current 

 gave oscillogram No. 3. 



One object in taking these oscillograms, together with the voltage- 

 phase cycle, was to see if there is any evidence of lag of the rectified 

 cycle with respect to the voltage-phase cycle. No such lag appears. 

 On the other hand, the rectified cycles lead their respective voltage- 

 phase cycles at three positions : 



The first of these positions of lead is at the part of the cycle in which 

 the rectified current approaches the zero axis after having traversed the 

 upper half of the curve. This advance, which is so small as to be just 

 perceptible in the oscillograms, amounts to about 1/6000 of a second. 



A second, somewhat larger, lead of the rectified cycle ahead of the 

 voltage-phase cycle is at the point of rising from the axis after the rec- 

 tified current has followed for a half period along the zero axis. The lead 

 here is about 1/1500 second. 



A third, very significant, lead of the rectified cycle is at the negative 

 maximum, as is seen in the cases of imperfect rectification, oscillograms 

 Nos. 2 and 3. Here the lead is a large fraction of a half period. 



Oscillogram No. 4 — Carborundum. — Oscillogram No. 4 was ob- 

 tained with a carborundum rectifier consisting of a specimen of car- 

 borundum, platinized on one side, and held in a clamp under a contact 

 pressure of 3 Kg. When sufficient current was sent through the car- 

 borundum to give deflections suitable for the oscillogram, the carborun- 

 dum was overloaded, and permitted current to pass in the negative 

 direction. The carborundum cycle differs from the molybdenite cycle 

 in the absence of lead at the negative maximum and at the point of 

 rising from the zero axis. This anomaly in the case of the carborun- 

 dum rectifier is seen later to be the effect of its high resistance. 



Oscillogram No. 5 — Brookite. — The form of the cycle obtained in 

 this case is intermediate between the carborundum cycle and the cycle 

 of oscillogram No. 3. This is consistent with the value of its resistance. 



In order to investigate the meaning of the lead of the rectified cycles 

 in the several cases, a further examination of the oscillograms is made 

 with the aid of the theory of alternating currents. 



