THE EMERGENCE OF THE STEAM THRESHING ENGINE


| November/December 1979



Steam engine

Princeton, Wisconsin 54968

A person is taught a heap of nonsense in a lifetime, much of it on supposedly good authority. In school you were probably taught that Watt invented the steam engine. Now there is some truth in this statement, but it is far from the whole truth. Yet your teacher probably never stopped to question the assertion, and it is unlikely you did either. What you should have been taught was that the steam engine emerged from the sweat and work of Watt and many other men, most of whom have received little, if any, public acclaim.

James Watt (b. 1736-d.l819) did not make the first devise for harnessing steam power. Centuries before Watt, the Greeks had devised simple models; and later steam power had been used to open and close cathedral doors. Robert H. Thurston, one of the best known authorities on the steam engine, described the state of the steam engine of 1700 in these terms:

'Every essential fact and every vital principle had been learned, and every one of the needed mechanical combinations had been successfully effected. It was only requisite that an inventor should appear, capable of perceiving that these known facts and combinations of mechanism, properly illustrated in a working machine would present to the world its greatest physical blessing.' (Robert H. Thurston, A History of the Growth of the Steam Engine, 1878, p. 56.)

The man who effected the combinations of which Thurston wrote was Thomas Newcomen, a blacksmith of Deptford, England. About 1705 Newcomen built an engine that functioned by means of a rocker arm situated above a cylinder in such a way that it could activate a water pump used to remove water from the mines of Britain. The cylinder set upright above the boiler and was open at its upper end. Steam entered the cylinder from below, and when the pressure was great enough the piston would rise within the cylinder. When the piston reached the top of the cylinder a jet of cold water was sprayed into the cylinder reducing the pressure and creating a vacuum. This caused the atmospheric pressure to depress the cylinder so that the cycle could be repeated. As a consequence of the use of both steam and atmospheric pressure, these kinds of engines were sometimes called atmospheric steam engines.

At first a Newcomen engine could make six to eight strokes per minute. With improvement some engines reached as many as a dozen strokes per minute. There was no flywheel, no governor, and steam was applied to only one side of the piston. The earlier boilers were made of copper. Subsequently sheet iron was used. The steam space within the boiler was about 8 to 10 times the capacity of the cylinder. It was a simple machine but it had several characteristics of later steam engines.