118 Mr Patterson, On the effect of a magnetic field 



On the effect of a magnetic field on the resistance of thin 

 metallic films. By J. Patterson, B.A., Toronto, 1851 Exhibition 

 Scholar. (Communicated by Professor Thomson.) 



[Read 4 March 1901.] 



A. C. Longden in the Physical Review, xi. 2. 40, described a 

 method of making standard high resistances from thin films of 

 metals deposited on glass by means of the kathode discharge. He 

 has shewn that the resistance of these films is much greater than 

 that calculated from the ordinary specific resistance of the metal. 

 It would be of interest to try what effect a magnetic field would 

 have on the resistance of a thin film deposited in this manner 

 from a bismuth kathode. 



The apparatus for making the films was the same as that used 

 by Longden. To secure good contact between the film and the 

 electrodes, the ends of the glass plates were silvered in a silvering 

 solution and fine copper wire was wound round the silvered ends ; 

 then copper was deposited electrolytically on the wire and on part 

 of the silver. The bismuth film was deposited on the glass plate 

 thus prepared. 



The films were examined under the microscope to see if there 

 was any visible discontinuity, but none could be detected, and as 

 there were no interference fringes produced by the reflected or 

 transmitted light the films were continuous to the order of the 

 wave-length of light. They were also tested by removing half 

 the width of the film, the resistance was then doubled, shewing 

 that the contacts with the electrodes were good and that, if there 

 were any discontinuities in parts of the film, they were equally 

 distributed. 



The thickness of the films was measured by Wiener's method 

 (Wied. Anii. 31. 629) and the measurements are correct to 15 per 

 cent. 



The resistance was measured by the ordinary Wheatstone 

 bridge and a D'Arsonval galvanometer, which had a resistance of 

 100 ohms and gave a deflection of 1 mm. on the scale for 2 x 10 -9 

 ampere. 



