Circular silver-plated commemorative medallion. commemorating the Invention of James Watt Steam Engine, made by D Thomason, England, 1800-1825. On the obverse is a central diagram of a steam engine, a history of James Watt's invention and the legend 'MR. WATT'S SINGLE ACTING STEAM ENGINE'. The reverse continues the explanation of the steam engine. The maker's name is near the rim. The edge is plain. Maker's name on reverse 'THOMASON.D.'