12. But when the nature of the thing requires that a motion is to be suddenly communicated to a body, or suddenly stopped: to prevent any damage or violence to the engine by a sudden jolt, let the force act against some spring, or beam of wood, which may supply the place of a spring.
13. In regard to the size of the machine, let it be made as large as it can conveniently; the greater the machine, the more exact it will work, and perform all its motions the better; for there will always be some errors in the making, as well as in the materials, and consequently in the working of the machine. The resistance of the medium in some machines has a sensible effect; but all these mechanical errors bear a less proportion in the motion of great machines, than in that of little ones; being nearly reciprocally as their diameters, supposing they are made of the same matter, and with the same accuracy, and are equally well finished.
14. For engines that go by water, it is necessary to measure the velocity, drop in pieces of sticks, &c. and observe how far they are carried in a second, or any given time.
But if it flows through a hole in a reservoir, or standing receptacle of water, the velocity will be found from the depth of the whole below the surface.
Thus let s = 16¹⁄₁₂; v = velocity of the fluid per second; B = the area of the hole; H = the height of the water; all in feet. Then the velocity of v = √2 s H; and its force = the weight of the quantity vv2sB or H B of water, or = 62¹⁄₂112H B hundred weight: because a cubic foot = 62¹⁄₂ lb. avoirdup. Also a hogshead is about 8¹⁄₂ feet, or 531lb. and a tun is 4 hogsheads.
When you have but a small quantity of water, you must contrive it to fall as high as you can, to have the greater velocity, and consequently more force upon the engine.
15. If water is to be conveyed through pipes to a great distance, and the descent be but small, much larger pipes must be used because the water will come slow.
Water should not be driven through pipes faster than four feet per second, by reason of the friction of the tubes; nor should it be too much wire-drawn, that is, squeezed through smaller pipes, for that creates a resistance, as water-way is less in narrow pipes.
16. When any thing is to be performed by a water-wheel, moved by the water running under it and striking the paddles or ladle-boards, the channel it moves in ought to be something wider than the hole of the adjutage, and so close to the floats on every side as to let little or no water pass; and when past the wheel, to open a little, that the water may spread. It is of no advantage to have a great number of floats or paddles; for those past the perpendicular are resisted by the back water, and those before it are struck obliquely. The greatest effect that such a wheel can perform, in communicating any motion, is when the paddles of the wheel move with one-third the velocity of the water; in which case, the force upon the paddle is four-ninths only; supposing the absolute force of the water against the paddle, when the wheel stands still, to be 1: so that the utmost motion which the wheel can generate, is but ⁴⁄₂₇ths of that which the force of the water against the paddles at rest would produce.
MADRAS. Fort St. George. A town and fort on the Coromandel coast, in the East Indies, belonging to the English. The town is called Madras by the inhabitants, but by the natives, Chilipatam. It is divided into two towns, the one called the White, and the other the Black town; the former being inhabited by Europeans, and the latter by Gentoos. The diamond mines of Golconda are a week’s journey from this place. The town is governed by a mayor and aldermen, with other officers. It is 63 miles north of Pondicherry, lat. 13, 5, N. long. 80, 34, E. It may not be irrelevant to state, that the establishments belonging to Great Britain, on the coast of Coromandel, is divided into several governments, independent of each other. Bombay commands the factories on the western side of the peninsula, commonly called the Malabar coast; together with those in Guzzerat: the establishments and possessions on the eastern or Coromandel coast, are under the government of Madras; and those in Bengal depend on Calcutta.