CONTENTS.

Article		Page
480.	The potential function A mathematical expression used to calculate the force at any point in a field. resulting from a straight current. It is a function with multiple values.	130
481.	The action of this current compared with that of a magnetic shell A theoretical thin sheet magnetized perpendicularly to its surface. possessing an infinite straight edge and extending infinitely on one side.	131
482.	A small circuit acts at a great distance like a magnet.	131
483.	Deducing from this the action of a closed circuit of any shape and size on any point not located within the current itself.	131
484.	Comparison between the circuit and a magnetic shell.	132
485.	Magnetic potential of a closed circuit.	133
486.	Conditions required for the continuous rotation of a magnet around a current.	133
487.	The shape of magnetic equipotential surfaces Surfaces where the magnetic potential is the same at every point. produced by a closed circuit. See Figure 18.	134
488.	Mutual action between any system of magnets and a closed current.	135
489.	The resulting reaction force exerted back upon the circuit.	135
490.	The force acting on a wire carrying a current when placed within a magnetic field.	136
491.	Theory of electromagnetic rotations.	138
492.	The action of one electric circuit upon the whole or any part of another.	139
493.	Our method of investigation follows that of Michael Faraday.	140
494.	Illustration of this method as applied to parallel currents.	140
495.	Dimensions The fundamental physical units (length, mass, time) that define a measurement. of the unit of current.	141
496.	The wire is pushed away from the side where its magnetic action strengthens the existing magnetic force, and toward the side where it opposes it.	141
497.	The action of an infinite straight current on any other current located in the same plane.	142
498.	Statement of the laws of electromagnetic force. The magnetic force produced by a current.	142
499.	The universal application of these laws.	143
500.	The force acting on a circuit placed within a magnetic field.	144
501.	Electromagnetic force is a mechanical force acting on the physical conductor, not on the electric current itself.	144

CHAPTER II.

THE MUTUAL ACTION OF ELECTRIC CURRENTS.


502.	Ampère’s investigation into the law of force between the individual elements Infinitesimal segments or parts. of electric currents.	146