Henry Letheby

 ( 1816 Births ) 

Letheby designed an interrupter circuit for use with for the medical application of electricity. The function of an interrupter circuit is to continually make and break the supply to the induction coil, which causes the coil to generate a large back emf at its output each time it is switched. Early interrupters were operated by hand, but Golding Bird introduced an automatic interrupter which worked electromagnetically in 1838. The problem with Bird's interrupter, and the problem that Letheby wished to solve, was that the direction of flow of the electric current was in opposite directions during the make and the break operations. Medical applications of electricity often required a unidirectional current, particularly when treating nervous disorders. Letheby's design caused only either the make or the break current to flow to the patient by a mechanical arrangement of two spoked wheels. Letherby proposed that a further advantage of his machine was that the pulses from the make contact provided a rather lesser shock to the patient than the pulses from the break contact. This gave the physician some control in situation where large shocks were not needed.Iwan Rhys Morus, Frankenstein's Children: Electricity, Exhibition, and Experiment in Early-nineteenth-century London, pp. 250–251, Princeton University Press, 1998 .Henry Letheby, "A description of a new electro-magnetic machine adapted so as to give a succession of shocks in one direction", Medical Gazette, p. 858, 13 November 1846.
Summarised in The Retrospect of Practical Medicine and Surgery, no.15, pp. 81–82, January–July 1847.