Elliptical gears were explained briefly in No. 67. Steam enters at the top from a boiler, exerts pressure on the arms of gears, and the pistons rotate. As arms pass exhaust pipe entrance in turn, steam passes into the air. When used as a pump, the action is the same as in No. 150.
[Virginia Downward & William M. Clark, 1930]

[Editor's Note: The principal application of the rotary engine today is the Wankel engine in the Mazda sports car. However in the 19th century there were many other variations such as this elliptical pump-engine. Clark copied this model after Figure 429 in Henry T. Brown's 1868 catalog of mechanical movements. Brown attributes this design to a patent of Holly. These rotary mechanisms can be used as either pumps or engines. In the Reuleaux collection of mechanisms there is a series of models I-1 to I-9 that are similar to the Clark rotary pump/engine model. FCM]

Francis Moon 2005-00-00