In this machine, as well as Vauloue's, the motion of the first wheel is uninterrupted, so that very little time is lost in the operation: with a slight alteration it might be made to work with horses. It has the advantage over Vauloue's engine in point of simplicity; it may be originally constructed at less expence, and is not so liable to be deranged. Both, however, are ingenious performances, and part of their construction might be advantageously introduced into other machines.

PIPES, for conveying of water, for pumps, water-engines, &c. are usually of lead, iron, earth, or wood: the latter are usually made of oak or elder. Those of iron are cast in forges; their usual length is from six to eight feet: several of these are commonly fastened together by means of four screws at each end, with leather or old hat between them, to stop the water. Those of earth are made by the potters; these are fitted into one another, one end being always made wider than the other. To join them the closer and prevent their breaking, they are covered with tow and pitch: their length is usually about that of the iron pipes. The wooden pipes are trees bored with large iron augers of different sizes, beginning with a less, and then proceeding with a larger successively; the first being pointed, the rest being formed like spoons, increasing in diameter from one to six inches or more: the pipes are fitted into the extremities of each other (as represented in pl. XXII. fig. 1.), and are sold by the foot.

Wooden pipes are bored either by a borer advancing horizontally while the wood to be pierced is turned round, in some such manner as in boring of ordnance; or, by causing the timber to be gradually advanced, while the borer turns round: the latter method is the most common. The apparatus most frequently adopted, when the first mover is a stream of water, is that invented by M. Morel, and described by Belidor (Architecture Hydraulique, tom. I.) This machinery is represented at pl. XXII. fig. 1. where the vertical wheel a is put into motion by water descending upon it through a trough or sloping canal: upon the horizontal axle of this wheel is a cog-wheel B, which gives motion to the lanterns C, D, the common axis of these lanterns being in a vertical position. The lantern D turns at the same time two cog-wheels E and F: the first, E, which is vertical, turns the auger that bores the wood: and the second, F, which is horizontal, has attached to it by a pin which is at a small distance from its centre, a lever or arm H, with a hook at its end, taking into the indentations of one of the wheels of the carriage that carries the wood to be bored. Another lever, 1, hanging upon the former, is prevented from falling by a spring, and pushes by its extremity against the notches of the lower end

of the same wheel. Thus, as the cog-wheel turns round, the carriage-wheel is first pulled forward by the hook and lever H, and then pushed backward as far by the arm 1; by this means causing a pinion upon the axle of the carriage-wheel to advance the rackwork above it, together with the timber to be bored: so that the timber is advanced by a slight reciprocating motion of the carriage. The auger, being generally some feet in length, plays in holes in two pieces L, L, which retain it in its horizontal position; and thus it forms a cylindrical cavity in the wood, as required.

For an account of the ingenious method of boring stone pipes employed at the Fox-Hill Quarry, in Gloucestershire, see the article PIPE in the PANTOLOGIA.

PLANET WHEELS are wheels by whose mutual connection a variable angular motion, such as that of the radius vector of a planet in its orbit, may be exhibited. The common contrivance now in use for this purpose was invented, we think, by Desaguliers: it consists of two elliptical wheels connected either by teeth running into each other, or by a band; these wheels revolve on their foci, and while the driving ellipses move uniformly, the radius vector of the other has the required motion.

A much older, and at the same time far better, method than that of Desaguliers, is described in the first volume of the Recueil des Machines et Inventions approuvées par l'Acad. Roy. des Sci. 1699: it was the invention of M. Joli de Dijon. The following account of this method is translated from the work just mentioned.

If it be desired to move a wheel of 24 teeth by a pinion of 6, in such a manner that in some parts of its revolution it shall move as swiftly as if it had but twelve teeth, and in other parts as slowly as if it had 48 teeth, the method of accomplishing this is as follows:

1. Describe the rectangle LMNO (fig. 1. pl. XXIII.) having its side No equal to the radii of the great wheel and the pinion taken together, and its breadth LN equal to their thickness; which last must be greater the more considerable the inequality of the proposed movement. Let No be so divided in o, that 90 may be to ON as 6 to 48, that is to say, reciprocally as the velocity of the pinion to the greatest velocity of the wheel. Also divide LM in P in the proportion of 6 to 12, or reciprocally as the velocity of the pinion to the least velocity of the wheel. Then join Po, and draw as many lines SR parallel to LM, as there are intended to be teeth in the great wheels; upon which write the degrees of velocity they express, which are in the inverse ratio of their lengths.

2. Let two truncated cones be formed in the lathe; one equal to that which would be formed by the revolution of the trapezoid LPQN about LN as an axis; and the other equal to what would be formed by the revolution of the trapezoid POMO about the axis MO. On the largest of these two cones let the circles generated by the revolution of the points P, T, Q, be marked and distinguished by the same numeral figures as the corresponding parallels of the rectangle Lo. Upon the two bases of the conic frustum describe radial lines, which shall make angles at the centre (fig. 3.) in the same proportion to each other as the intended velocities of the wheel, as expressed in fig. 2. and let teeth be cut in the curve surface of the cone corresponding with these lines: after this, look on the circles that express the different velocities, and have been traced on the same surface, to find what part of each tooth ought to remain opposite its corresponding radius, and cut or file the rest away. Thus will the teeth lie in an oblique or elliptical curve on the conical surface, as is exhibited in the figure by a darker shade. The pinion must be made of a regular conic shape, as is shewn at Mo in fig. 3.

By this contrivance the largest or widest teeth will always meet the largest part of the pinion, and the narrowest will correspond with the smallest part: on which account, though the motion of the pinion be uniform, the wheel will be carried unequably, according to the assigned law.

In a similar manner may planet-wheels be described to exhibit any other proposed variation.

PRESS, a machine of wood, or iron, serving to squeeze any body very close.

Presses usually consist of six pieces: two flat smooth planks, between which the things to be pressed are laid; two screws or worms fastened to the lower plank, and passing through two holes in the upper; and two nuts in form of an s, that serve to drive the upper plank, which is moveable, against the lower, which is fixed. See BRAMAH's Machine.

PRESSES used for expressing Liquors are in most respects the same with the common presses, only the underplank is perforated with a great number of holes for the juice to run through. Others have only one screw, or arbor, passing through the middle of the moveable plank, which descends into a kind of square box full of holes, through which the juices flow as the arbor is turned.

PRESS used by Joiners to keep close the pannels, &c. of wainscot, consists of two screws, and two pieces of wood, four or five inches square, and two or three feet long, whereof the holes at two ends serve for nuts to the screws.

Founders' PRESS, is a strong square frame, consisting of four pieces of wood firmly joined together with tenons, &c. It is of various sizes: two of them are required to each mould at the two extremes whereof they are placed; so as that, by driving wooden wedges between the mould and sides of the press, the two parts of the mould for the metal may be pressed close together.

PRESS, binders' cutting-, is a machine used equally by bookbinders, stationers, and pasteboard-makers; consisting of two large pieces of wood in form of cheeks, connected by two strong wooden screws; which, being turned by an iron bar, draw together, or set asunder, the cheeks, as much as is necessary for the putting in the books or paper to be cut. The cheeks are placed lengthwise on a wooden stand in form of a chest, into which the cuttings fall. Aside of the cheeks are two pieces of wood of the same length with the screws, serving to direct the cheeks, aud prevent their opening unequally. Upon the cheeks the plough moves, to which the cutting-knife is fastened by a screw; which has its key, to dismount it, on occasion, to be sharpened.

The plough consists of several parts; among the rest, a wooden screw or worm, which, catching within the nuts of the two feet that sustain it on the cheeks, brings the knife to the book or paper which is fastened in the press between two boards. This screw, which is pretty long, has two directories, which resemble those of the screws of the press. To make the plough slide square and even on the cheeks, so that the knife may make an equal paring, that foot of the plough where the knife is not fixed slides in a kind of groove, fastened along one of the cheeks. Lastly, the knife is a piece of steel, six or seven inches long, flat, thin, and sharp, terminating at one end in a point, like that of a sword, and at the other in a square form, which serves to fasten it to the plough.

As the long knives used by us in the cutting of books or papers are apt to jump in the cutting thick books, the Dutch are said to use circular knives with an edge all round; which not only cut more steadily, but last longer without grinding.

Various other presses are used in different arts and manufactures; but it does not seem necessary to give particular descriptions of any others, except the press used in printing of books, and the rolling press used in copper-plate printing.

The common PRINTING-press represented in pl. XXIII. is a curious and rather complex machine. The body consists of two strong cheeks, a, a, standing perpendicularly, and joined together by four cross pieces; the cap 6, and the head c, which is moveable, being partly sustained by two iron pins or long screw

bolts that pass the cap; the till or shelf dd, by which the spindle and its apparatus are kept in their proper position; and the winter e, which bears the carriage, and sustains the effort of the press beneath. The spindle f is an upright piece of iron pointed with steel, having a male screw, which goes into the female one in the head about four inches. Through the eye g of this spindle is fastened the bar k, by which the pressman makes the impression. The spindle passes through a hole in the middle of the till; and its point works into a brass pan or nut, supplied with oil, which is fixed to an iron plate let into the top of the platen. The body of the spindle is sustained in the centre of an open frame of polished iron, 1, 1, 2, 2, 3, 3, fixed to it in such a manner as, without obstructing its free play, to keep it in a steady direction; and at the same time to serve for suspending the platen. This frame consists of two parts: the upper called the garter, 1, 1; the under called the crane, 2, 2. These are connected together by two short legs or bolts, 3, 3; which being fixed below in the two ends of the crane, pass upward through two holes in the till, and are received at top into two eyes at the ends of the garter, where they are secured by screws. The carriage is placed a foot below the platen, having its fore-part supported by a prop called the fore-stay, while the other rests on the winter. On this carriage, which sustains the plank, are nailed two long iron bars or ribs; and on the plank are nailed short pieces of iron or steel called cramp-irons, equally tempered with the ribs, and which slide upon them when the plank is turned in or out. Under the carriage is fixed a long piece of iron called the spit, with a double wheel in the middle, round which leather girts are fastened, nailed to each end of the plank and to the outside of the spit is fixed a rounce m, or handle, to turn round the wheel. Upon the plank is a square frame or coffin, in which is inclosed a polished stone on which the form n is laid; at the end of the coffin are three frames, viz. the two tympans and the frisket: the tympans o are square, and made of three slips of very thin wood, and at the top a piece of iron still thinner; that called the outer tympan is fastened with hinges to the coffin: they are both covered with parchment; and between the two are placed blankets, which are necessary to take off the impression of the letters upon the paper. The frisket p is a square frame of thin iron, fastened with hinges to the tympan: it is covered with paper cut in the necessary places, that the sheet, which is put between the frisket and the great or outward tympan, may receive the ink, and that nothing may hurt the margins. To regulate the margins, a sheet of paper is fastened upon this tympan, which is called the tympan sheet; and on each side is fixed an iron point, which makes two