PIERCE. — CRYSTAL RECTIFIERS FOR ELECTRIC CURRENTS. 319 



surfaces of contact, while the other surface was left unplatinized, gen- 

 erally rendered the rectification more nearly perfect. This fact indi- 

 cated that the seat of the action was the area of contact with the 

 electrodes, and that the action at the two contacts were in opposition 

 to each other, so that when the action at one of the contacts was re- 

 duced by platinizing, the rectification at the other contact appeared 

 more pronounced. 



These characteristics of the phenomenon are consistent with the 

 view that the rectification is conditioned on the localization of the energy 

 of the circuit at the high resistance boundary between the two different 

 classes of conductors, the crystal and the metallic electrode. 



Now such a localization of energy at the boundary of the two con- 

 ductors is favorable to the production of electrolytic polarization, if we 

 may have electrolytic polarization in solids, and is also favorable to the 

 production of a thermoelectromotive force, either of which might result 

 in rectification. 



Nevertheless, in Part I, a number of experiments are described which 

 were taken to indicate that neither electrolysis nor thermoelectricity 

 plays an important part in the phenomenon. 



On the question of electrolysis, the following experiment, performed 

 since the publication of Part I, has a bearing. 



Experiment showing Permanence of the Carborundum Rectifier. — 

 In confirmation of the absence of electrolytic polarization, a durability 

 test of the rectifier has later been made as follows : A crystal of car- 

 borundum enclosed in a glass tube with a few drops of oil 3 and held 

 between brass electrodes, one of which was under tension of a spiral 

 spring, was kept under almost daily observation 4 from October 23, 

 1907, until March 18, 1908. During this time more than 1200 measure- 

 ments were made of the direct current obtained through the crystal under 

 different direct and alternating voltages. The rectifier was kept in a 

 thermostat and subjected to various long periods of heating and cooling 

 ranging from 0° to 80° C. Notwithstanding the long continued expo- 

 sure of the crystal to large changes of temperature, and notwithstand- 

 ing the frequent loading and occasional overloading of the rectifier with 

 current, it was found at the end of the series that the values of the di- 

 rect current obtained from the crystal under a given applied alternating 

 voltage over a range of current from 4 to 400 microamperes (direct) 



3 The oil served to prevent accumulation of moisture. 



4 This series of measurements was carried out by Mr. K. S. Johnson, to whom 

 the writer wishes to express his sincere thanks. The experiment was finally dis- 

 continued on account of the accidental melting of the cement holding in the ends 

 of the tube. 



