The progress of physics during 33 years (1875-1908) : four lectures delivered to the University of Calcutta during March 1908 / by Arthur Schuster.

  • Arthur Schuster
Date:
1911
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Licence: In copyright

Credit: The progress of physics during 33 years (1875-1908) : four lectures delivered to the University of Calcutta during March 1908 / by Arthur Schuster. Source: Wellcome Collection.

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    fore be an electric current through the non-conducting space between the plates A and B when the battery is connected, but only while the plates are charging. When this is done there is no further current through any part of the circuit. The question which now arises, is whether the current which can temporarily pass through a non-conducting medium has all the pro- perties of an ordinary electric current, more especially its electro-magnetic properties. Maxwell assumes that it has, and this carries with it the consequence, that a change of magnetic force causes an induced current in a non-conducting as well as in a conducting medium. Here then we have a generalisation which is sufficiently precise to allow of its being followed up mathematically and being confirmed or disproved by experiment. If at some point of space a change of electric force takes place, as for instance when an electrified con- ductor be moved backward and forward, there must, if Maxwell is right, be electric currents in that part of the medium which immediately surrounds the conductor ; and these again must act by electro-magnetic induction on the other adjacent parts of the medium. The problem is quite definite and leads to a system of equations for the propagation of an electrical disturb- ance, giving a constant rate of propagation, which can be calculated. The numerical data which are necessary for the purpose are obtained by comparing, e.g. in the above example (Fig. i) the electro-magnetic force of the charging current with the electrostatic attraction between the plates, when fully charged. It