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| xxii | CONTENTS. |
| Art. | Page |
|---|---|
| 818. Kinetic and potential energy of the medium | 406 |
| 819. Condition of wave-propagation | 406 |
| 820. The action of magnetism must depend on a real rotation about the direction of the magnetic force as an axis | 407 |
| 821. Statement of the results of the analysis of the phenomenon | 407 |
| 822. Hypothesis of molecular vortices | 408 |
| 823. Variation of the vortices according to Helmholtz's law | 409 |
| 824. Variation of the kinetic energy in the disturbed medium | 409 |
| 825. Expression in terms of the current and the velocity | 410 |
| 826. The kinetic energy in the case of plane waves | 410 |
| 827. The equations of motion | 411 |
| 828. Velocity of a circularly-polarized ray | 411 |
| 829. The magnetic rotation | 412 |
| 830. Researches of Verdet | 413 |
| 831. Note on a mechanical theory of molecular vortices | 415 |
Chapter XXII.
Electric Theory of Magnetism
| 832. Magnetism is a phenomenon of molecules | 418 |
| 833. The phenomena of magnetic molecules may be imitated by electric currents | 419 |
| 834. Difference between the elementary theory of continuous magnets and the theory of molecular currents | 419 |
| 835. Simplicity of the electric theory | 420 |
| 836. Theory of a current in a perfectly conducting circuit | 420 |
| 837. Case in which the current is entirely due to induction | 421 |
| 838. Weber's theory of diamagnetism | 421 |
| 839. Magnecrystallic induction | 422 |
| 840. Theory of a perfect conductor | 422 |
| 841. A medium containing perfectly conducting spherical molecules | 423 |
| 842. Mechanical action of magnetic force on the current which it excites | 423 |
| 843. Theory of a molecule with a primitive current | 424 |
| 844. Modifications of Weber's theory | 425 |
| 845. Consequences of the theory | 425 |
Chapter XXIII.
Theories of Action at a Distance.
| 846. Quantities which enter into Ampère's formula | 426 |
| 847. Relative motion of two electric particles | 426 |
