William McNaught (1813–1881) was a Scottish engineer, from Glasgow, who patented a compound steam engine in 1845.
This was a technique of improving the efficiency of a standard simple Boulton & Watt beam engine.
The engine was compounded by adding a high-pressure cylinder between the support column and the flywheel, on the side opposite the low-pressure cylinder.
This improvement could be retrospectively fitted to existing engines.