PIERCE. — CRYSTAL RECTIFIERS FOR ELECTRIC CURRENTS. 349 



current and the thermal current renders the correctness of the thermo- 

 electric explanation of the phenomenon of rectification extremely im- 

 probable. 



Effort to detect Heating of the Contact of the Rectifier. — With the 

 aid of the auxiliary thermal junction of copper-constantan placed at the 

 contact of the copper with the molybdenite, as shown in Figure 12, an 

 effort was made to detect heating of the copper molybdenite junction 

 by the alternating current which was being rectified. When the recti- 

 fied current was 118 microamperes, the heating shown by the copper- 

 constantan junction did not exceed .01° C. When, on the other hand, 

 as a control experiment, heat was applied to the copper-molybdenite 

 junction from below so as to be conducted through the molybdenite and 

 through the copper-molybdenite junction to the copper-constantan 

 junction, the heating shown by the auxiliary copper-constantan junc- 

 tion was 11.4° C, while the thermal current from the copper-molyb- 

 denite junction was only .2 microamperes. In both the case of the 

 rectified current and the case of the application of heat from below the 

 heat had to be conducted from the point of rectification to the auxiliary 

 junction. Therefore, with a rise of temperature of the auxiliary junc- 

 tion 1100 times as great as the rise shown during the rectification, the 

 thermal current in the copper-molybdenite circuit was 1/500 of the 

 rectified current ; that is to say, the rectified current, for a rise of tem- 

 perature of 1/100 of a degree of the auxiliary junction (being approxi- 

 mately a linear function of the temperature) was less than 1/500000 of 

 the rectified current from an alternating current producing the same 

 rise of temperature. 



From this experiment, also, it seems to the writer that the hypothesis 

 that the action of the rectifier takes place through the intermediation 

 of thermoelectricity is improbable. Experiments are still in progress. 



I have been aided in this investigation by a liberal grant from the 

 Bache Fund of the National Academy, for which I wish to express my 

 hearty thanks. 



Jefferson Physical Laboratory, 

 Harvard University, Cambridge, Mass., 

 December 21, 1908. 



