IV. Fig. 3.) that takes hold of the ram Q by the staple R LECT. for drawing it up. D is a spiral or fusy fixed to the drum, on which is wound the small rope that goes over the pulley U, under the pulley V, and is fastened to the tope of the frame at 7. To the pulley block V is hung the counterpoise W, which hinders the follower from accelerating as it goes down to take hold of the ram: for, as the follower tends to acquire velocity in its descent, the line T winds downwards upon the fusy, on a larger and larger radius, by which means the counterpoise Wacts stronger and stronger against it; and so allows it to come down with only a moderate and uniform velocity. The bolt Y locks the drum to the great wheel, being pushed upward by the small lever 2, which goes through a mortise in the shaft A, turns upon a pin in the bar 3 fixed to the great wheel B, and has a weight 4, which always tends to push up the bolt Y through the wheel into the drum. L is the great lever turning on the axis m, and resting upon the forcing bar 5, 5, which goes down through a hollow in the shaft A, and bears up the little lever 2. By the horses going round, the great rope His wound about the drum C, and the ram Q is drawn up by the tongs F in the follower G, until the tongs comes between the inclined planes E; which, by shutting the tongs at the top, opens it at the foot, and discharges the ram, which falls down between the guides b b upon the pile P, and drives it by a few strokes as far into the mud as it can go; after which, the top part is sawed off close to the mud, by an engine for that purpose." Immediately after the ram is discharged, the piece 6 upon the Note 41. When the piles are driven for the purpose of constructing a coffer-dam, they may be afterwards raised by the hydrostatic press of Bramah. The plan has been successfully adopted in many cases, and its advantage over our author's mode of sawing them beneath the water, will be sufficiently obvious, when we come to a description of that instrument. LECT. follower G takes hold of the ropes a, a, which raise the end of the lever L, and cause its end N to descend and press down the forcing bar 5 upon the little lever 2, which by pulling down the bolt Y, unlocks the drum C from the great wheel B; and then, the follower, being at liberty, comes down by its own weight to the ram; and the lower ends of the tongs slip over the staple R, and the weight of their heads causes them to fall outward, and shuts upon it. Then the weight 4 pushes up the bolt Y into the drum, which locks it to the great wheel, and so the ram is drawn up as before. As the follower comes down, it causes the drum to turn backward, and unwinds the rope from it, whilst the horses, great wheel, trundle, and fly, go on with an uninterupted motion: and as the drum is turning backward, the counterpoise W is drawn up, and its rope T wound upon the spiral fusy D. There are several holes in the under side of the drum, and the bolt Y always takes the first one that it finds when the drum stops by the falling of the follower upon the ram; until which stoppage, the bolt has not time to slip into any of the holes. This engine was placed upon a barge on the water, and so was easily conveyed to any place desired.-I never had the good fortune to see it, but drew this figure from a model which I made from a print of it; being not quite satisfied with the view which the print gives. I have been told that the ram was a ton weight, and that the guides bb, between which it was drawn up and let fall down, were 30 feet high. I suppose the great wheel might have had 100 cogs, and the trundle ten staves or rounds; so that the fly would make ten revolutions for one of the great wheel." Note 42. Engines of this description, although much simplified, are now very generally employed; not merely in the construction of bridges and other branches of hydraulic architecture, but also in the manufacture of buttons, and other purposes connected with the arts. The operation of the pile engine may be best understood by refer- LECT ence to a former note in which the doctrine of accelerated motion is IV. examined, and it may be only necessary to add, that the momentum thus acquired is exactly equivalent to so much additional weight falling upon the head of the pile. Note 43. The following additional illustration of the preceding subjects will be found valuable to the practical artizan, and they have been introduced at the close of the Lecture to prevent an unnecessary interference with our Author's text. There are four principal modes of employing the force of water as a prime mover in machinery, and of these the under and over-shot water-wheels, are the most important: of the other two, namely, the breast-wheel and Barker's mill, but little need be said, as the latter is but seldom resorted to, and the breast wheel may be considered but as a modification of the two preceding. The following diagrams will best illustrate the under and over-shot water-wheels. The over-shot wheel it will be seen owes its power to the weight of the water, while the under-shot, on the contrary, depends on its impulse. In order to determine the effect of any force employed in machinery, we must consider not only its magnitude, but also the velocity with which it can be brought into action, and we must estimate the ultimate value of the power, by the joint ratio, or the product, of the force and the velocity. Thus, if we had a corn-mill, for example, in which we wished the mill-stone to re |