PIERCE. — CRYSTAL RECTIFIERS FOR ELECTRIC CURRENTS. 347 



An auxiliary thermal junction formed by a small constantan wire 

 attached to the lower end of the copper rod C was connected to a second 

 galvanometer shown at G, for use in a latter experiment. 



TABLE XI. 



Sign of Molybdenite when heated Above or Below and 

 when subjected to alternating voltage. 



The copper rods C or E could be heated by the surrounding coils, 

 and the thermal current in the circuit through the molybdenite or the 

 circuit through the constantan could be read on the galvanometers A 

 or G. Also the rectified current obtained by applying the alternating 

 voltage V could be read on the galvanometer A. When the thermal 

 current or the rectified current through A is in the direction of the 

 arrow B, the molybdenite, following the usage in thermoelectricity, is 

 said to be positive. When the current in A is in the direction opposite 

 to the arrow B, the molybdenite is said to be negative. 



The results obtained with a number of specimens of molybdenite 

 when heat was applied above, and when heat was applied below, 



