The interrupter is included in series with the main primary circuit of the coil, the current passing through the mercury and shaft of the motor, by way of the revolving metal disc. It is sometimes advised that the contacts of the platinum break should be screwed together, and the mercury interrupter included externally in the circuit. This, however, is inadvisable, as by so doing the function of the condenser is destroyed. The correct way is to connect, as usual, the source of current with the main terminals of the coil, to separate the contacts of the platinum break, and then to connect the mercury interrupter to the respective pillars of the latter, for which purpose terminals should be provided for the base of the coil. The condenser is then not short circuited, with the result that the full effect is produced with the coil.

Here, as with platinum breaks, however, let care be taken not to render the period of contact longer than is absolutely necessary to effect the full degree of magnetization of the iron core, for the reason explained above. It should be borne in mind that the inductive effect between the primary and secondary windings occurs only at the moment of the alternate make and break of the current, and no advantage is to be derived from a continuous flow of current. To obviate risk, therefore, of this occurrence, especially when accumulators constitute the source of energy, the period of contact when the current is switched on, should be small, and then gradually increased until the desired effect is obtained. - "English Mechanic."