. Annual report of the Board of Regents of the Smithsonian Institution. Smithsonian Institution; Smithsonian Institution. Archives; Discoveries in science. 134 LIGHT AND ELECTRICITY. itself, if that is not broken. In other words, a cnrrent will persist after the cessation of its causes, just as a moving body does not stop the instant it is no longer driven forward. When, then, the two potentials become e(j[ual, the current will go on and give the two conductors relative charges opposite to those they had at first. In this case, as in that of the pendulum, the position of equi- librium is i^ass
. Annual report of the Board of Regents of the Smithsonian Institution. Smithsonian Institution; Smithsonian Institution. Archives; Discoveries in science. 134 LIGHT AND ELECTRICITY. itself, if that is not broken. In other words, a cnrrent will persist after the cessation of its causes, just as a moving body does not stop the instant it is no longer driven forward. When, then, the two potentials become e(j[ual, the current will go on and give the two conductors relative charges opposite to those they had at first. In this case, as in that of the pendulum, the position of equi- librium is i^assed, and a return motion is inevitable. Equilibrium, agjiin instantaneously attnined, is at once again broken for the same reason; and so the oscillations pursue one another unceasingly. Calculation shows that the period depends on the cajiacity of the con- ductors in such a way that it is only necessary to diminish that capacity sufnciently (which is easily done) to have an electric pendulum capable of producing an alternating current of extremely short period. All that was well enough known by the theoretical researches of Lord Kelvin and by the experimentation of Federsen on the oscillatory discharge of the Leyden jar. It was not that which constituted the originality of Fk;. 1.—The liertz cxoitor. But it is not enough to construct a i^endulum; it is further requisite to set it into oscillation. For that, it is necessary to carry it off from equilibrium and to let it go suddenly, that is to say, to release it in a time short as compared to the i)eriod of its oscillation. For if, having pulled a pendulum to one side by a string, we were to let go of the string more slowly than the pendulum would have descended of itself, it would reach the vertical without momentum, and no oscillation would be set up. In like manner, with an electric i)endulum whose natural period is, say, a liundred-millionth of a second, no mechanical mode of release would answer the purpose at all
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