On the Colours of Mixed Plates. 679 



Corbino constant, c, related to the Hall coefficient, R, by 

 c = kTi, where k is the specific conductivity, was found 

 to be, for magnetic fields between 50 and 1000 e. m. units, 

 c = 6"5 . 10 " 7 . This is about the same value as was previously 

 found for magnetic fields up to 8000 units. 



The apparent reversal obtained by Dr. Chapman appears 

 to have been due to currents induced in the solenoid circuit 

 by the reversed radial disk current, thus inducing currents 

 in the test-coils placed next to the disk. In order to regu- 

 late the solenoid current for the small values of the magnetic 

 field additional rheostats were employed, and these were 

 sufficiently near the circuit carrying the radial di>k current 

 to produce the spurious effects. The mutual inductance 

 between the circuits varied with the position of the sliders of 

 the rheostats, and complicated effects were thus produced 

 which were superimposed upon the true Oorbino effect. 

 That this was the case could be shown by short-circuiting 

 the disk current leads at the disk, keeping all the rest of 

 the circuit unchanged. Any mutual induction between the 

 solenoid circuit and the disk circuit was then shown by effects 

 of the same nature as the Corbino effect. On separating 

 the two circuits sufficiently this effect was made wholly to 

 disappear, and on allowing the radial current to flow through 

 the disk the true Corbino effect was obtained with the results 

 already stated. 



1 wish to thank Mr. W. C. Duryea, mechanician of the 

 laboratory, for the construction of a really satisfactory double 

 commutator. 



Palinsr Physical Laboratory, 

 Princeton, N. J. 



LXXV1IL Onthe Colours of Mixed Plates,— -Part III. By 

 0. V. PtAMAN, M.A., Palit Professor of Physics, and 

 K. Seshagim Rao, B. A. (Hons.), Research Scholar^ 

 University of Calcutta *. 



1. Introduction. 



A DETAILED description of the phenomena exhibited 

 by mixed plates, including several features of interest 

 not previously noticed, was given in the first paper of 

 the series f. In the second paper J it was shown by a 



* Communicated by the Authors. 

 t Phil. Mag. March 1921, p. 338. 

 X Phil. Mag. June 1921, p. 860. 



