THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[FIFTH SERIES.] 



DECEMBER 1876. 



L. On Bi- and Unilateral Galvanometer Deflection. By Gr. 

 Chrystal, B.A., Fellow of Corpus Christi College, Cam- 

 bridge*. 



I WAS led to study the subject of this paper during a series 

 of experiments undertaken for the purpose of directly 

 testing Ohm's law. 



The results arrived at are, I think, interesting, not only 

 in connexion with galvanometry, but also in relation to the 

 theory of induced magnetism. In the first instance I shall 

 describe the phenomena as simply as possible from the first 

 point of view, and then consider a little more closely some 

 points which arise when the matter is looked at from the second 

 point of view. This order is to a great extent that in which 

 the facts came under my notice ; and it has the additional ad- 

 vantage that it leads us incidentally to see that the phenomena 

 in question really have their seat solely and entirely within the 

 galvanometer, and have nothing to do with any phenomenon 

 of the nature of unilateral conductivity or with any other ex- 

 ception to Ohm's law. 



Dr. Schuster has described f an experiment in which a 

 small current of constant direction is superposed on the alter- 

 nating currents of a sine inductor, and the whole sent through 

 a galvanometer. Such an experiment affords (under certain 

 suppositions) a test of Ohm's law ; for the average intensity 

 of the current in the direction of the small constant current is 

 greater than that in the opposite direction ; hence, if the re- 



* Communicated by the Author. 

 t Phil. Mag. [IV.] Vol. xlviii. p. 340. 



Phil Mag. S. 5. Vol. 2. No. 13. Dec. 1876. 2 D 



