WITH ELECTROMAGNETIC FORCE. 



129 



equation of the potential of two coils, given at p. 508 * of my paper on the 

 Electromagnetic Field, 



d*M d*M 1 dM 



_| _ Q /5\ 



do? db* a da 



('2\ 

 1 iV-rJ, where a is the depth 

 a / 



of the coil a correction which is in this case about 1 "000926. 



A. Suspended disk and coil. 



A'. Counterpoise disk and coil. 



C. Fixed disk and coil. 



B,. Great battery. B a . Small battery. 



G,. Primary coil of galvanometer. 



Secondary coil. R. Great resistance. 



Torsion head and tangent screw. 



One quarter of the micrometer-box, disks, and coils is cut away to shew the interior. The case of the 

 instrument is not shewn. The galvanometer and shunts were 10 feet from the Electric Balance. 



G, 

 T. 



K. Double key. g. Graduated glass scale. 

 C'. Electrode of fixed disk. 



x. Current through R. 



x. Current through G,. x x'. Current through S. 



y. Current through the three coils and G 2 . 

 S. Shunt. M. Mercury cup. 



* [Vol. i. p. 591.] 



VOL. II. 



17 



