Curved brass casting with one cylindrical and two flat faces, by James Watt, Glasgow, Scotland, 1758-1769. Used as the divider of the drum of a rotary steam engine.
This item is part of the contents of the workshop that Scottish engineer James Watt developed at his home, Heathfield, at Handsworth, Birmingham. Although Watt is best known for his work on the steam engine, his workshop contains a wide variety of objects from many different projects, from chemistry to sculpture-copying.
The description of the item was written by Edward Collins, the land agent responsible for Heathfield when the workshop was given to the Science Museum in 1924. Collins could not always identify what he was looking at, but always described what he saw clearly. This has allowed his descriptions to form the basis of subsequent research.
These are fragments of Watt's 1782 rotary steam engine. Watt, as well as constructing traditional steam engines using beams, also attempted to make an engine without a piston and cylinder, using pure rotary motion. In this, a steam jet spun the three blades around a shaft. Although it leaked and hit technical difficulties, Matthew Boulton wrote excitedly that ‘if we had a hundred wheels ready made’ he could easily sell them. It was premature – an effective rotary steam engine did not arrive until 1884 with the Parsons turbine.
This item is a block of cast brass, intended as the divider of the drum of Watt's 1782 rotary steam engine. One face is cylindrical, and was meant to lie against the wall of the drum. The other two faces are flat, but formed at different angles to the radius. The longer face would have formed a “ramp” up which the jointed vanes would have rubbed, before dropping off the end and swinging out to meet the wall of the drum again. The shorter face is cut away to form an open channel of circular section, which presumably corresponded to the hole through which steam would have been admitted. The design is naïve, in that the jointed vanes would have met the ramp with a blow; this face would better have been incurved. The other faces are as-cast, and there are no fixing holes.