The hammer break is usually operated by the magnetism of the iron core of the coil, but for some reasons it is better to separate the break from the coil altogether, and to work it by an independent electromagnet, which, however, may be excited by a current from the same battery supplying the induction coil.
"Hertzian Wave Wireless Telegraphy"
John Ambrose Fleming
The mercury interrupter may be worked by a separate electromagnet or by the magnetism of the core of the induction coil.
"Hertzian Wave Wireless Telegraphy"
John Ambrose Fleming
The author has found that, without the use of any air blast or electromagnet, simple adjustment of the double choking coil in the primary circuit of the transformer, as above described, is sufficient to bring about the desired result, when the capacity of the condenser is adjusted to be in resonance.
"Hertzian Wave Wireless Telegraphy"
John Ambrose Fleming