Page:A Treatise on Electricity and Magnetism - Volume 2.djvu/17

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  CONTENTS. xi
Art. Page
503. His method of experimenting 146
504. Ampère's balance 147
505. Ampère's first experiment. Equal and opposite currents neutralize each other 147
506. Second experiment. A crooked conductor is equivalent to a straight one carrying the same current 148
507. Third experiment. The action of a closed current as an element of another current is perpendicular to that element 148
508. Fourth experiment. Equal currents in systems geometrically similar produce equal forces 149
509. In all of these experiments the acting current is a closed one 151
510. Both circuits may, however, for mathematical purposes be conceived as consisting of elementary portions, and the action of the circuits as the resultant of the action of these elements 151
511. Necessary form of the relations between two elementary portions of lines 151
512. The geometrical quantities which determine their relative position 152
513. Form of the components of their mutual action 153
514. Resolution of these in three directions, parallel, respectively, to the line joining them and to the elements themselves 154
515. General expression for the action of a finite current on the element of another 154
516. Condition furnished by Ampère's third case of equilibrium 155
517. Theory of the directrix and the determinants of electrodynamic action 156
518. Expression of the determinants in terms of the components of the vector-potential of the current 157
519. The part of the force which is indeterminate can be expressed as the space-variation of a potential 157
520. Complete expression for the action between two finite currents 158
521. Mutual potential of two closed currents 158
522. Appropriateness of quaternions in this investigation 158
523. Determination of the form of the functions by Ampère's fourth case of equilibrium 159
524. The electrodynamic and electromagnetic units of currents 159
525. Final expressions for electromagnetic force between two elements 160
526. Four different admissible forms of the theory 160
527. Of these Ampère's is to be preferred 161