This is an early medical induction coil from around 1873. The coil is 9”x 3” conical shaped wooden surrounded by four brass terminal posts and electro magnetic interrupter coil at side. It has an iron wire core that pulls in and out to adjust intensity.
An induction coil or "spark coil" is a type of electrical transformer used to produce high-voltage pulses from a low-voltage direct current supply. Voltage is repeatedly interrupted by a vibrating mechanical contact called an interrupter . They were widely used in medical electrotherapy devices from the 1880s to the 1920s. .
Made of mahogany, all original.
The plaque at the top reads: “Griggs Conical Electro Magnetic Machine, Patented Jan. 8th 1873, 33 Eastbourne Terrace Hyde Park London. Maker JR. Chislett, Plymouth”.