The rapidity of the opening of the primary circuit in the coils with the hammer circuit breaker was improved by Armand Hippolyte Louis Fizeau (1819-1896) by deriving a condenser between the reed and the point. In this way, most of the energy that would be delivered to the contacts, thus generating a spark and deteriorating them, is stored in the condenser and the formation of the spark is avoided, or in any case greatly attenuated; the interruption of the current in the primary is thus incomparably faster and in the secondary there are much higher induced tensions.
The speed with which the primary current opens in Ruhmkorff coils was further improved by using circuit breakers that were not of the hammer type, such as the mercury one which was invented by Foucault and which will be described in the following article.