CONTENTS.

Article		Page
663.	Mathematical expression for the effect of the induced currents	269
664.	Case of the uniform motion of a magnetic pole	269
665.	Value of the force acting on the magnetic pole	270
666.	Case of curvilinear motion Motion along a curved path.	271
667.	Case of motion near the edge of the sheet	271
668.	Theory of Arago's rotating disk A phenomenon where a rotating copper disk causes a suspended magnetic needle to rotate, discovered by François Arago in 1824.	271
669.	Trail of images in the form of a helix A spiral shape.	274
670.	Spherical current-sheets	275
671.	The vector-potential	276
672.	To produce a field of constant magnetic force within a spherical shell	277
673.	To produce a constant force on a suspended coil	278
674.	Currents parallel to a plane	278
675.	A plane electric circuit. A spherical shell. An ellipsoidal shell	279
676.	A solenoid A coil of wire acting as a magnet when carrying electric current.	280
677.	A long solenoid	281
678.	Force near the ends	282
679.	A pair of induction coils	282
680.	Proper thickness of wire	283
681.	An endless solenoid	284

CHAPTER XIII.


682.	Cylindrical conductors	286
683.	The external magnetic action of a cylindrical wire depends only on the total current through it	287
684.	The vector-potential	288
685.	Kinetic energy The energy of motion. of the current	288
686.	Repulsion between the direct and the return current	289
687.	Tension of the wires. Ampère's experiment	289
688.	Self-induction of a wire doubled on itself	290
689.	Currents of varying intensity in a cylindrical wire	291
690.	Relation between the electromotive force and the total current	292
691.	Geometrical mean distance of two figures in a plane	294
692.	Particular cases	294
693.	Application of the method to a coil of insulated wires	296


694.	Potential due to a spherical bowl	299
695.	Solid angle subtended by a circle at any point	301