At the beginning of this century not more than "four engines of any importance" were at work in the whole continent of America: of these one supplied New York with water, another gave motion to a saw-mill, and the other two belonged to the corporation of Philadelphia.*

In 1804 Mr. William Lushington introduced one of Mr. Watt's engines into the colony of Trinidad, and we believe that the expense of its work was estimated at about one third only of the same quantity of labour performed by the cattle-mills commonly used in the colony.†

An ingenious combination of Savery's and Papin's apparatus was proposed in 1805, by Mr. James Boaz of Glasgow. The Forty-second Figure shews one of his arrangements, by which water can be raised without condensing the steam. a, is the steam cylinder; i, the pipe from the boiler, having a stop-cock; k, a waste steam cock; e, a floating piston attached to a piston-rod. E a pipe which generally contains hot water; f water pipe, having a valve at g immersed in the well, and delivering the water into the reservoir o, through a valve, z. The air which accucontact, and consequent resistance to the moving from the fixed parts. Besides, as the stuffed parts are here of great extent with regard to the magnitude of the machinery, and exhibit rapid variations of shape, they may, when brought into constant work, be found difficult to keep in order." Note by Dr. Gregory.—The specification is printed at length in the Repertory of Arts.

* Historical Account of Steam Engine, p. 46.

+ Trinidad is stated in this account to be the first West India Colony, in which the Steam Engine was introduced; but we believe that in Jamaica they were in action many years before this period.

mulates in the receiver escapes at n; o, the raised water cistern; d, rarifying or exhausting vessel.

The whole being filled with mercury and water, shut the air-valve s, and open i; the steam from the boiler will rush into the receiver, and, after heating the water, it presses on its surface, forcing the mercury up into the exhausting vessel d, where it is shewn in the engraving by a darker shade. The water above c, and in the pipes e, f, will be forced up into the cistern v, in a quantity nearly equal to the space occupied by the steam in the receiver. When the piston has been depressed as far as is necessary for its stroke, the self-acting mechanism attached to its rod, shuts i, and opens k; and the mercury now being at liberty to act by its gravity, descends from the exhausting pipe, and raises the piston to its first position; and the steam which pressed it downwards being now allowed to flow into the atmosphere, the fall of the mercury from d, into a, leaves a vacuum in d, into which the water from the well is pressed by the atmosphere, and again fills it. The valve at g, prevents its return to the well in the operation of forcing; and the valve %, prevents its fall from the cistern when the vacuum is made in d.*

The rotative Engine (the Forty-third Figure,) constructed by Mr. Andrew Flint, consists of two concentric cylinders or drums, placed at a certain distance from each other. To the inner cylinder is fixed a piston p, moving and made steam-tight in the space x, between the cylinders; and it is

* Repertory of Arts, vol. VIII. p. 322. Second Series

attached to two hollow axes y, z. The inner cylin

der is divided in its height into two chambers,

e, f; having two openings g, h. i, k, are two valves, which are moved alternately by levers acted on on the outside from the revolution of a spanner or lever attached to the hollow axle, one being always open when the other is shut.

The valve i, in the plan, being shut, and k open, and the piston in the situation shewn in the Figure, the steam issues through h, and impels the piston towards k; the air which may be in the space on the other side of the piston, escaping through g, into the chamber f, which communicates with the condenser. When the piston has passed valve k, it is shut; the steam will then be confined to the space between it and the piston, and will continue to impel the piston forward; the air still escaping as before on the other side of the piston through the movable aperture g, so that the quantity of steam impelling the piston can never be more than half the contents of the channel of revolution; it is then admitted into the vacuum made on the other side of the piston, and drawn off by the condenser. The idea is ingenious; but the friction must be enormous. Mr. Robert Willcox's Engine,* differs from Mr. Flint's only in the mode of placing the cocks, and the position of the pipes from the boiler and condenser.

In his rotative Engine, Mr. Mead, in place of the cylinders substitutes shells, or a circular ring in which the pistons move; and instead of making the apertures for the admission of steam, and its exit to the con

* 1806.