Hand-coloured ink and watercolour drawing showing elevations, cross-sections and plan views of several key components of an atmospheric condensing beam pumping engine designed by James Watt and supplied by the firm Bolton & Watt, of Birmingham, to the Margaret Mine, at Wanlockhead, Scotland, in 1785-86. Scale: 1/4 inch to 1 inch. Undated, but likely 1785. The drawing is part of a set of technical drawings supplied by the manufacturers showing details of key components for a 55-inch (1397 mm) bore x 8 foot (2438 mm) stroke single-acting single-cylinder steam pumping engine ordered by Gilbert Meason, general manager of the Wanlockhead Mining Company for the Margaret Mine in June 1785. Labelled as sheet No.7, it shows (at upper left) details of the crop bar for the air pump with details for attachment of linkages and top of the valve plug, (at lower left) details of the gland on the king post of the engine beam, (at upper right) details of Martingales for the piston rod and air pump and for the plug rod and condenser pump rods on the engine beam, and (at lower right) details of the great gland on the main gudgeon on the engine beam. Martingales are iron stays that form distinctive diagonal braces between the curved sectors and main beam as shown in sheet No.1 (ST 041088). The drawing is believed to have been executed by James Watt, or an assistant working under his direction, and includes a number of annotations written in blue ink in what appears to be Watt's hand, giving selected dimensions and other notes to the erectors.

The engine depicted was built to replace a smaller 36-inch (914 mm) bore Boulton & Watt pumping engine erected in 1778-79, which was found to be too underpowered to cope with the drainage load as the mine workings went deeper. At the time that both Watt engines were built for the Wanlockhead mines, Boulton & Watt had not yet established their Soho Foundry (1795), and it was their general practise to just supply drawings for the erection of their engines and organise for the supply of key components from a number of third-party engineering firms across northern England and the midlands. Generally a skilled erector would be sent by Boulton & Watt to supervise installation and commissioning of each engine, but in the case of the Wanlockhead engines, none of Boulton & Watt's regular experts were available, so the work was left in the hands of the mining company's engineer George Symington, assisted by his younger brother, William Symington. The experience would provide one of the most important formative events in the subsequent career of twenty-one year old William, and would help set him on the course of a life-long interest in the applications and improvements of steam technology.

Wanlockhead is a historic mining village situated in the Lowther Hills region of the Scottish Southern Uplands, at the head of the Mennock Pass. It is noted for being Scotland's highest village at an average elevation of 1,531 feet (467 m) above sea level. The area has been exploited since at least Roman times for its mineral resources, which include deposits of lead, zinc, copper, silver and gold. The current village was founded in 1680 when Sir James Stampfield built a lead smelting plant and workers' cottages. Beam pumps powered by a self-acting water bucket were introduced to drain the Wanlockhead mines in 1745. The Wanlockhead Mining Company was formed by Ronald Crawford and associates in 1755, and energetically exploited the area's rich lead veins over the following sixty years, working deposits to depths of over 540 feet (165 m), and producing 47,420 tons of lead. They were the first Scottish mine owners outside the Edinburgh coalfields to adopt seam powered pumping technology.

William Symington appears to have kept several of the original Wanlockhead Steam Engine drawings as a memento of his involvement and would later pass them onto his second-oldest son, William Symington junior (c.1802-1867), who bought the surviving drawings to Australia when he emigrated in 1855. They were subsequently donated to Museum Victoria by a descendant of the family.

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Scaled (1/4 inch to 1 inch), coloured (brown, grey, black) technical line drawing annotated with handwritten text and dimensional details in black and red ink, and pencil. The drawing shows details of key components of a steam beam engine in plan and elevation views.

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