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 to most persons that some power can be obtained from a jet of steam either by the reaction of the jet itself, like a rocket or by its impact on some kind of paddle wheel. About the year 1837 several reaction steam wheels were made by Avery at Syracuse, New York, and by Wilson at Greenock, for driving circular saws and cotton gins. Fig. 3 shows the rotor of Avery's machine: steam is

Fig. 3. Rotor of Avery's Turbine.

introduced into it through a hollow shaft, and, by the reaction of the jets at the extremities, causes rotation. The rotor was 5 feet across, and the speed 880 feet per second. These wheels were inefficient, and it is not so obvious that an economical engine could be made on this principle. In the year 1888 Dr de Laval of Stockholm undertook the problem with a considerable measure of success. He caused