THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[FIFTH SERIES.] 



SEPTEMBER 1887. 



XXVII. On some Methods of Determining and Comparing 

 Coefficients of Self-induction and Mutual Induction. By 

 Prof. 0. Niven, F.R.S.* 



§ 1. T>R0F. CAREY FOSTER'S paper, published in the 

 J- Philosophical Magazine (February 1887), has lately 

 recalled attention to the methods of comparing or determining 

 coefficients of induction by means of the galvanometer. He 

 has shown how to express the coefficient of induction of two 

 coils in terms of the capacity of a condenser. The problem 

 there presented is one of several which arise in the comparison 

 of the three kinds of transient currents which are met with 

 (1) in the charge of condensers, (2) in the mutual induction 

 of two circuits, (3) in the self-induction of a circuit. 



Of the corresponding problems which occur in the compa- 

 rison of electrical constants three may be looked upon as still 

 somewhat imperfectly solved. These are the comparison of 

 two coefficients of self-induction, the comparison of a coeffi- 

 cient of self-induction of a coil with that of mutual induction 

 between any other two coils, and the determination of a coeffi- 

 cient of self-induction in terms of the capacity of a condenser. 

 Prof. Chrystal has indeed given, in his paper on the Differen- 

 tial Telephone, various solutions of the last ; but his methods 

 involve the use of the telephone, while Maxwell's method in 

 this case requires that a single adjustment should secure both 

 no steady current through the galvanometer and no transient 

 current. The same remark applies to his method of com- 

 paring the coefficients of self-induction of two coils ; and his 



* Communicated by the Author. 



Phil. Mag. S. 5. Vol. 24. No. 148. Sept. 1887. Q 



