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| xvi | CONTENTS. |
| Art. | Page |
|---|---|
| 639. The force acting on a particle of a substance due to its magnetization | 251 |
| 640. Electromagnetic force due to an electric current passing through it | 252 |
| 641. Explanation of these forces by the hypothesis of stress in a medium | 253 |
| 642. General character of the stress required to produce the phenomena | 255 |
| 643. When there is no magnetization the stress is a tension in the direction of the lines of magnetic force, combined with a pressure in all directions at right angles to these lines, the magnitude of the tension and pressure being , where is the magnetic force | 256 |
| 644. Force acting on a conductor carrying a current | 257 |
| 645. Theory of stress in a medium as stated by Faraday | 257 |
| 646. Numerical value of magnetic tension | 258 |
Chapter XII.
Current-Sheets.
| 647. Definition of a current-sheet | 259 |
| 648. Current-function | 259 |
| 649. Electric potential | 260 |
| 650. Theory of steady currents | 260 |
| 651. Case of uniform conductivity | 260 |
| 652. Magnetic action of a current-sheet with closed currents | 261 |
| 653. Magnetic potential due to a current-sheet | 262 |
| 654. Induction of currents in a sheet of infinite conductivity | 262 |
| 655. Such a sheet is impervious to magnetic action | 263 |
| 656. Theory of a plane current-sheet | 263 |
| 657. The magnetic functions expressed as derivatives of a single function | 264 |
| 658. Action of a variable magnetic system on the sheet | 266 |
| 659. When there is no external action the currents decay, and their magnetic action diminishes as if the sheet had moved off with constant velocity | 267 |
| 660. The currents, excited by the instantaneous introduction of a magnetic system, produce an effect equivalent to an image of that system | 267 |
| 661. This image moves away from its original position with velocity | 268 |
| 662. Trail of images formed by a magnetic system in continuous motion | 268 |
