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| CONTENTS. | xxiii |
| Art. | Page |
|---|---|
| 848. Relative motion of four electric particles. Fechner's theory | 427 |
| 849. Two new forms of Ampère's formula | 428 |
| 850. Two different expressions for the force between two electric particles in motion | 428 |
| 851. These are due to Gauss and to Weber respectively | 429 |
| 852. All forces must be consistent with the principle of the conservation of energy | 429 |
| 853. Weber's formula is consistent with this principle but that of Gauss is not | 429 |
| 854. Helmholtz's deductions from Weber's formula | 430 |
| 855. Potential of two currents | 431 |
| 856. Weber's theory of the induction of electric currents | 431 |
| 857. Segregating force in a conductor | 432 |
| 858. Case of moving conductors | 433 |
| 859. The formula of Gauss leads to an erroneous result | 434 |
| 860. That of Weber agrees with the phenomena | 434 |
| 861. Letter of Gauss to Weber | 435 |
| 862. Theory of Riemann | 435 |
| 863. Theory of C. Neumann | 435 |
| 864. Theory of Betti | 436 |
| 865. Repugnance to the idea of a medium | 437 |
| 866. The idea of a medium cannot be got rid of | 437 |
