This dynamo model was introduced by the company Mather & Platt of Manchester in 1885 and had later a wide diffusion. Its lower and upper poles are symmetrical and cast each one into a single iron part, respectively with the base plate and with the supports on the excitation coil cores. The airgap magnetic flux distribution is more uniform than in the previous machines of this kind.
The rotor is drum-shaped and the holes in the rotor iron, for the winding, are closed. The same factory began in 1888 the production of the 4-pole dynamos that led in a few years to the final shape, more economical and efficient of the direct current dynamo.
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The one shown here was made by the Swiss
factory, Oerlikon, on a project by the engineer