The drawing that is the subject of the photograph is a finely detailed and rendered illustration of the Whitbread engine. At the time the photograph was taken, the engine was known to be significant as an early example of the rotative engines made by the ground-breaking firm of Boulton and Watt.
The engine is now recognised as the oldest rotative engine in the world, so the photograph is significant as a record of how the engine appeared in its final form at Whitbread's London brewery. It completes a record that begins in the holdings of the Birmingham City Archives with drawings, dated 1784, of the proposed engine; continues with drawings in the same collection showing the engine's conversion from single-acting to double-acting in 1795; and includes a drawing by John Farey, created around 1812 for Rees' Cyclopaedia, of the engine and the brewery equipment it powered.
Unfortunately, the caption below the photograph perpetuates the myth that the engine's output was originally 35 horsepower and that this was doubled to 70 horsepower in 1795. These figures were included in a plaque that was once attached to the engine but which probably never left England. It ascribed the invention of the steam engine to Edward Somerset and celebrated the contributions of Thomas Savery, Thomas Newcomen and John Cawley, John Smeaton, and James Watt and Matthew Boulton, to the engine's improvement. From other evidence, both documentary and based on the bore and stroke of the engine, the engine's original output was closer to 10 horsepower and its final output was 15 or 16 horsepower.
The photograph represents the esteem in which Whitbread & Co held the engine even as it decided to dispose of it. This esteem was shared by Professor Archibald Liversidge and led him to request that the engine be donated to the Museum.
Debbie Rudder, August, 2007