This is a three-quarter size replica of the Reverend Robert Stirling’s innovative ‘Air Engine’, shown by Geoff Goodchild at the 2017 Bristol exhibition.

A recent book by Stirling authority, James Rizzo, describes in detail the two earliest surviving hot air engines, and how to build working replicas, or reduced sized models of them. It is published by Camden.

The two engines concerned are those which Robert Stirling presented to the University of Edinburgh, and slightly later, to the University of Glasgow, to demonstrate his 'Air Engine'. The exact dates these were built is not known, but certainly before 1825. The Edinburgh model is the more original, as the Glasgow model was discovered in an old store by Prof. William Thomson, later Lord Kelvin, in 1847. He dismantled it to see how it worked, and restored it to working order; along the way establishing the Absolute Scale of Temperature, the term ‘energy’ and invented the name of a new science - Thermodynamics.

Both models are now very fragile, but Mr Rizzo was granted unprecedented access to measure and inspect them by both Universities. From the resulting drawings he made half-size models of both engines, but while the building instructions here refer to these models, the drawings are dimensioned full size, with metric and decimal inch measurements for accurate conversion. Hardwoods were used extensively in the original engines. Other than, possibly, for the flywheel (12 inch diameter in the original), no castings are required.