Page:Elementary Text-book of Physics (Anthony, 1897).djvu/328

314 that if a Leyden jar be discharged through a circuit, it will momentarily produce thermal, chemical, and magnetic effects which are similar to those just described as produced continuously by the voltaic battery.

The discharge of the jar may be variously represented. So long as electricity is considered as a fluid or substance, it is easiest to think of the discharge as the transfer of electricity from a place of higher to a place of lower potential, or rather as the equalization of potential by the transfer of equal and opposite quantities in opposite senses, and to explain the continuous effects produced by the voltaic battery by ascribing them to a current, or continuous transfer of electricity around the circuit. This view is capable of representing most of the phenomena of steady or permanent currents, but it is less successful in representing the phenomena of variable currents. If we consider electrical phenomena as due to actions in the dielectric, we may obtain a more adequate representation of the discharge and also of all the phenomena of the current by the use of the unit tubes of force described in § 265. We may obtain some idea of the connection of these tubes with the current if we examine their behavior during the discharge of a condenser.

To make the discussion as simple as possible, we suppose the condenser to be made of two equal plates $$A$$ and $$B;$$ their potentials are $$V_{A}$$ and $$V_{B}, \, V_{A}$$ being the greater. The lines of force originate at $$A$$ and pass to $$B$$ in the manner shown in Fig. 83. This figure has been roughly copied from the one given by J. J. Thomson. Let $$Q$$ represent that part of the charge on $$A$$ to which corresponds an equal and opposite charge on $$B:$$ the number of unit tubes of force which pass from $$A$$ to $$B$$ will then be given by $$Q.$$ Now let us join $$A$$ to $$B$$ by a conductor $$C,$$ which for the sake of simplicity shall coincide with the direction of the lines of force. No tube of force can exist within a conductor, and those which were present in the volume which the conductor