Original model of surface condenser and air pump, probably made at Soho, Birmingham, in 1775, and presented by James Watt & Co.

This model, which was probably made very shortly after inv. 1876-1267, is complete, and shows an excellent surface condenser and air-pump. The separate condenser was the critical innovation upon which engineer James Watt's entire career building steam engines depended, and has been described as the 'greatest single improvement' ever made to steam engine design.