The construction of an hydraulic engine with powers nearly similar to this, may be thus described: two buckets of unequal size must be first suspended by a flexible chain turning on a double roller or pulley; so that one bucket will be elevated to the required height, while the other reaches the level of the water to be raised; a small stream of water must then be made to communicate with the largest bucket, which will speedily be depressed and descend to the lower level, while the opposite bucket will discharge its contents into a cistern or reservoir at the top of the machine: the larger bucket being likewise emptied by striking against a projecting beam placed there for that purpose. Mr. Sarjeant has described a very simple and powerful machine for raising water, nearly similar in point of principle to the above. An engraving of Mr. S.'s engine, together with an account of its construction, is inserted in the Trans. of the Soc. of Arts, vol. xix. p. 255. No. XXII. To make a river in a garden ebb and flow constantly, though twenty foot over, with a child's force, in some private room, or place out of sight, and a competent distance from it. NOTE. The very ingenious canal lock lately invented by Peter Bogaerts, Esq., appears fully calculated for effecting this object. In this lock, which from its simplicity is no less useful than economical, a small portion of water is made to assist in displacing several tons of that element, and there is no doubt but a _child's force_ would raise double the quantity of water described by the Marquis. In the model lately exhibited, a weight of seven pounds was made to raise 10 _cwt._ of water more than four feet in a few seconds. No. XXIII. To set a clock as within a castle, the water filling the trenches about it; which shall show, by ebbing and flowing, the hours, minutes, and seconds, and all the comprehensible motions of the heavens, and counterlibration of the earth, according to Copernicus. NOTE.