In consequence of the comparative precision which this improvement gave to its movements, as well as on account of the greater safety, and immense saving which was made in the quantity of fuel, when compared with that used by machines on Savery's principle, the use of the Atmospheric Engine had so extended as in a great degree to supersede the high-pressure engines.

Still many inconveniences remained to be removed; and not the least was the necessity of employing boys or men to open and shut some of the cocks for, although the risk of accident from the explosion of the boiler might now be considered to have been obviated, the effect of the engine depending much on the condition of its parts, and these being easily deranged by slight irregularities in their action, the danger of injury to the machine itself was considerably increased, from the ignorance or carelessness of the attendants.

The mechanism for opening and shutting the cocks also remained perplexed by catches and strings, until Mr. Henry Beighton, an engineer extensively employed in the construction of mining machinery, erected an engine at Newcastle-on-Tyne, in 1718, in which all these "cock-boys" and complication of cords were superseded by a rod suspended from the beam, which operated on a mechanism invented by him called hand-gear; a contrivance, with some slight modifications, employed in engines of the present day. It would also appear that the steelyard safety-valve was first used in the boiler of this engine, having been suggested to Beighton by Desaguliers.

The cylinder of the Griff Engine was 22 inches in diameter; and Beighton calculated that it con

tained 113 gallons of steam at every stroke, equal to about 14,464 gallons per minute, which was produced from about five pints of water; and this quantity was equal in its performance to three-fourths of the atmospheric pressure; so that, making allowance for the friction* of the piston, levers, and other parts, about eight pounds of water was raised by each square inch of the piston.

In examining the Seventeenth Figure, which is a view of the Atmospheric Engine as improved by Beighton, it will be seen, that, in addition to the hand-gear, he gave a better arrangement and form to the parts already in use, and paid more attention to the proportion of the parts among themselves, and to the work which they had to perform; besides introducing greater neatness and accuracy of workmanship into his engines than had been attempted by his predecessors.

In the Seventeenth Figure, the cistern, x, for the supply of injection water, is placed as in the previous engravings, and water is pumped into it by a small pump connected with the pipe, y, y, leading from the mine. (The lever beam, z, is not continued on the pump side beyond its axis, A, as this would have required our Figure to have been drawn on a scale much too small for being distinct.) To make the piston, d, air-tight, a ring or piece of match is laid upon its circumference; which is kept moist by a small stream of water kept constantly

* Tallow was used in these Engines to lessen the friction, but not to keep them air-tight.

+ The origin of packing the piston is thus given by Desaguliers:"Having screwed a large broad piece of leather to the piston which turned up the sides of the cylinder two or three

running from the pipe, s, upon the piston, d;-a projecting rim rising above the highest point to which the piston is elevated, prevents the water from flowing over the sides of the cylinder, when the piston has reached its upward stroke: this will also be observed in the preceding figures. The boiler which is shewn as cased in brick-work, is supplied with warm water from this rim by a pipe, b; the water falls into a funnel, g, attached to a pipe, g, which rises to a convenient height above the top of the brick-work, and descends about a foot into the water in the boiler; the two gauge-pipes, i, i, are used (as in Savery's Engine,) to ascertain the quantity of the water in the boiler; the lower end of one is immersed for a short distance in the water-the lower end of the other reaching to within a few inches of its surface. If steam issues from both cocks when they are opened, there is a deficiency of water in the boiler; if both give water, then it shews there is an overabundant quantity. The cold water is injected into the cylinder through a pipe, f; and after it has performed its office of condensation it is conducted by the pipe, t, t, and escapes through a valve at its

inches, in working it wore through and cut that piece from the other, which, falling flat on the piston, wrought with its edge to the cylinder, and, having been in a long time, was worn very narrow; which being taken out, they had the happy discovery, whereby they found that a bridle-rein, or even a soft thick piece of rope, going round, would make the piston air and watertight."-Desaguliers' Nat. Phil. Hornblower observes, "We need not say any thing to the practical engineer about leuthering a steam piston. Nor is it necessary to comment on the Doctor's acquaintance with steam and leather in contact."-Gregory, Mech. vol. ii. p. 358. 1st edition.