The mine was named Bay after Botany bay in Australia and lies just outside the village of Wanlockhead at NGR NS868137. 1789 saw the opening of the pumping/main shaft at Bay Mine. The mine appears to have operated from 1790 to 1919. This mine is famed for being the site of William Symington's Improved Atmospheric Engine. William Symington (1764-1831) was a Scottish engineer and inventor, and the builder of the first practical steamboat. William Symington saw a way to marry the efficiency of the Watt engine with the simplicity of that devised by Thomas Newcomen. He patented the idea in 1787. Steam was condensed under a second piston and this was then pushed down when fresh steam entered the cylinder, forcing out the condensate. The power piston worked by the atmospheric pressure acting on the vacuum created by the condensing steam. This resulted in the improved engine at Bay Mine in 1789 and Symington becoming known as the inventor of the commercially viable atmospheric pumping engine. The bob wall of Symingtons engine remains on site along with a large wheelpit and other structures around the main shaft.