338 PROCEEDINGS OF THE AMERICAN ACADEMY. 



(3) The very significant lead of the negative maximum ahead of the 

 corresponding voltage-phase maximum is explicable on the assumption 

 that the rectifier has a much higher resistance in the negative direction 

 than in the positive direction. We have seen above that the angle of 

 lag of the voltage-phase cycle behind the impressed voltage, determined 

 by the inductance and resistance of the circuit, is 



tan- 1 — — 35° 

 tan 836 ~ d5 ' 



while in the negative direction the substituted equivalent resistance 

 should be at least 6470 + 436 = 6906 ohms, whence the angle of lag 

 in this case would be 



Therefore, the angle of lead of the rectified cycle ahead of the voltage- 

 phase cycle, determined as the difference of these two angles of lag, is 

 30.2°. This value agrees with oscillogram No. 2. 



In this connection it is interesting to notice that a lead of this nega- 

 tive maximum in the case of the carborundum oscillograph does not 

 appear. The explanation of this is easily obtained if one substitutes 

 for the resistance values of the molybdenite the corresponding values 

 for the circuit containing the carborundum rectifier. The equivalent 

 resistance of the carborundum in its positive loop is 6000 ohms, so that 

 the angle of lag of the voltage-phase cycle with this resistance in it is 

 only 5.6°, while in the negative direction the equivalent resistance of 

 the carborundum is about 20,000 ohms, giving an angle of lag in the 

 neighborhood of 1°. The difference between these two angles of lag, 

 which would give the phase difference between the carborundum 

 cycle and the corresponding voltage-phase cycle, would be a quantity 

 just perceptible on the oscillogram, as was verified in the original 

 photographs. 



In conclusion of this discussion of the oscillograms, I should say that 

 we have not been able to detect in the photographs any evidence of a 

 thermoelectric or other integrative action of the rectifier. 



Thermoelectric Properties of Molybdenite. 



In the present section an account is given of the investigation of the 

 thermoelectromotive force of molybdenite against copper and a deter- 

 mination of the temperature coefficient of resistance of molybdenite. 

 Apart from their possible bearing on the action of the rectifier, the 

 thermoelectric properties of molybdenite are of interest in themselves. 



