with tappets for working levers in connection with the valves.
The accuracy of Desaguliers's account has been somewhat discredited of late years by the discovery of a copperplate print of an engine built by Newcomen in 1712. It was first brought to light at the loan collection of scientific apparatus held at South Kensington in 1876. It represents an atmospheric engine with wooden beam and arch-heads of the familiar type, and a plug-rod provided with tappets for working the injection and steam valves, being in every respect a self-acting machine. The cylinder was twenty-one inches diameter, and seven feet ten inches high. The engine made twelve strokes per minute, raising fifty gallons of water from a depth of 156 feet. From these data the engine was 5½ horse-power. The print is entitled ‘The Steam Engine near Dudley Castle. Invented by Capt. Savery and Mr. Newcomen. Erected by ye latter 1712. Delin. and sculp. by T. Barney, 1719.’ The explanatory matter is printed in letterpress on the side, the engraving having been printed from the copper on larger paper than required to give space for the letterpress. Only two copies are known, that shown at South Kensington being the property of Mr. Sam Timmins of Birmingham. The other copy, which is in the William Salt Library at Stafford, exhibits a different arrangement of the printed explanatory matter, and has in addition the imprint: ‘Birmingham: Printed and sold by H. Butler, New Street.’ The importance of this print in the history of the steam-engine was pointed out by the present writer in the ‘Engineer’ of 26 May 1876, and it is further discussed in R. L. Galloway's ‘Steam Engine,’ 1881, p. 84, where a reduced facsimile of the print is given. A facsimile appeared also in the ‘Engineer’ of 28 Nov. 1879. It furnishes the earliest known example of the beam engine, and is the first authentic record of the exact nature of Newcomen's improvements. The contrast between the machine described by Savery in his ‘Miner's Friend,’ published in 1702, and Newcomen's engine of 1712 is most remarkable. Newcomen invented an entirely new type of engine, and, though improvements were made in the details and workmanship, it continued to furnish the model for the pumping-engine for nearly three-quarters of a century. It was very gradually superseded by Watt's engine with separate condenser, patented in 1769.
The engine described by Desaguliers as having been made for Mr. Back of Wolverhampton is almost certainly the same as that represented in the print ‘near Dudley Castle.’ The dates exactly correspond, and the two places are only about six miles apart. On the other hand, Dr. Wilkes says that Newcomen ‘fixed the first [engine] that ever raised any quantity of water, at Wolverhampton, on the left-hand side of the road leading from Walsall to the town, over against the half-mile stone’ (Shaw, History of Staffordshire, vol. ii. pt. i. p. 120). This locality cannot properly be described as being ‘near Dudley Castle,’ but the reference may be to another engine. As will be seen by the extract from Desaguliers, he does not credit Newcomen with the invention of the self-acting gear, which was a very important improvement; but, as already pointed out, the engine near Dudley Castle was certainly self-acting. At p. 467 of his book he gives a slightly different account of the matter. ‘These discouragements,’ he says, ‘stopp'd the progress and improvement of this engine [i.e. Savery's], till Mr. Newcomen, an ironmonger, and John Cawley, a glazier, living at Dartmouth, brought it to the present form in which it is now used, and has been near these 30 years.’ This must have been written about 1743, the Royal Society's imprimatur being dated 17 Nov. 1743, which would take the matter back to 1713, a date approximating very closely to the date of erection of the engine represented in the print. The story of Humphrey Potter is now generally regarded as apocryphal, and it has been suggested that it was founded upon a misconception, a ‘buoy’ or float having been used in the early engines for opening the injection cock. One of the printed explanations in the print of the Dudley Castle engine runs: ‘Scoggen and his mate who work double to the boy.’
A minute technical account of the engine erected by Newcomen at Griff, near Coventry, about 1723, together with several plates, will be found in the work of Desaguliers already cited. The British Museum possesses a print, engraved by Sutton Nicholls in 1725, entitled ‘Description of the Engine for raising Water by Fire,’ which has much in common with the Dudley Castle engine. It is bound with a copy of I. De Caus's ‘New and Rare Invention of Water Works,’ 1704. Switzer gives a large view and description of a Newcomen engine, which he states is similar to that erected at York Buildings. Other engines are mentioned in Galloway's ‘Steam Engine,’ but it is not always easy to determine from the often imperfect descriptions given in county histories and similar works whether a particular machine was constructed on Savery's principle or on Newcomen's. To add to the difficulty,
