CONTRIBUTIONS FROM THE JEFFERSON PHYSICAL 

 LABORATORY, HARVARD UNIVERSITY. 



CRYSTAL RECTIFIERS FOR ELECTRIC CURRENTS AND 

 ELECTRIC OSCILLATIONS. 



II. CARBORUNDUM, MOLYBDENITE, ANATASE, BROOKITE. 



By George W. Pierce. 



Presented December 9, 1908. Received December 22, 1908. 



Table of Contents. 



Introduction 317 



Concerning Part I 317 



Questions arising in Connection with the Phenomenon 318 



Experiment showing Permanence of the Carborundum Rectifier . . . 319 



On the Question of a Possible Thermoelectric Origin of the Phenomenon 320 



Extension of the Experiments to Other Crystals 320 



Anatase and Brookite 320 



Anatase 320 



Brookite 321 



Molybdenite 321 



The Molybdenite Rectifier 322 



Current- Voltage Characteristic of the Molybdenite Rectifier 323 



Oscillographic Records of Rectified Cycle 226 



Method of obtaining the Oscillograms 326 



The Oscillographic Records 329 



Oscillograms Nos. 1, 2, and 3 — Molybdenite 330 



Oscillogram No. 4 — Carborundum 331 



Oscillogram No. 5 — Brookite 331 



Examination of the Oscillograms with the Aid of the Theory of 



Alternating Currents , 332 



Thermoelectric Properties of Molybdenite 338 



Thermoelectromotive Force 339 



Temperature Coefficient of Resistance 343 



Experimental Facts Adverse to the Thermoelectric Explanation 



of the Phenomenon of Rectification 346 



Thermoelectric Effect Opposite to the Rectification 346 



Effort to detect Heating of the Contact of the Rectifier 349 



Introduction. 



Concerning Part I. — Carborundum had been found by General 

 Dunwoody 1 to be capable of acting as a receiver for the electric waves 

 of wireless telegraphy. Having learned of this property of carborun- 



1 Dunwoody: U. S. Patent, No. 837,616, issued Dec. 4, 1906. 



