utility in raising water to supply towns, country seats, &c. or for other purposes, a wheel, on the principle here mentioned, might be used in such places to great advantage, as it would go either wholly under water, or partly so, and would always turn round the same way, whether the current was running down the river or up, as when affected by the tides, and therefore might be applied to tide-mills.

The flaps for water-wheels of this sort may be made either of thin deal or other boards, or of thin plates of metal. These water-wheels may be stopped or regulated by a sluice on either side, to stop the current, or to admit only so much as is thought necessary; and there may be other sluices to open at a suitable distance on both sides of the wheel, when the wheel sluices are shut.

Mr. Beatson proposes, likewise, to apply the same method of construction to several other objects and purposes, as to the pistons of pumps, oars, and sails for ships, ventilators, sluices, buckets for wells, &c. for a more particular description of which we must refer the reader to vol. ii. of the Repertory of Arts and Manufactures, second series, where Mr. Beatson's specification is published.

Another horizontal mill has been recently proposed by Mr. John Jackson; the following description of which has appeared in No. 4 of the Retrospect of Philosophical and Mechanical Discoveries, a very respectable and useful publication.

In this mill a stout vertical shaft carries two pairs of horizontal arms, crossing each other at right angles, so as to form suitable supports for the axles of four wheels carrying as many vanes, each placed at an equal distance from the vertical shaft, and at quadrantal distances from one to another. There are 9 toothed wheels arranged in the same horizontal plane, and mutually driving one another. The central wheel drives four others, which are called mean wheels; and these again, four others called extreme wheels: the mean and extreme wheels are attached to the arms by their axles, and are carried about with them when in motion; the extreme wheels are fixed to their axles, and the vanes are fixed to those axles, and consequently turn with them. These vanes are posited with respect to each other, in such manner that their planes make angles of 45°, 90°, 135°, and 180°, with some variable plane; so that while one vane is completely exposed to the wind, a second and fourth are opposed to it obliquely, and the third turns its end towards it, so as to offer but little resistance. Each of the extreme wheels has twice as many teeth as the central wheel; of consequence, during one revolution of the central wheel, each extreme wheel turns half round,

and each vane presents its sides alternately to the wind. The centre wheel consists of a drum or hollow shaft, through which the axle of the wheel passes. A handle is fixed to the lower extremity of the drum-shaft, by which the centre wheel is occasionally moved: this arm serves also as an index, and communicates with a circle, representing the horizon, on which are delineated the points of the compass. When the machine is in motion, the index is set and fastened to that point from which the wind blows, in order to adjust the position of the vanes with respect to the wind. Any motion of the index to the right or left of this point will alter the position of the vanes, and occasion a diminution of power in the machine; and it is by this index that the machine is stopped, or made to turn in a contrary direction; a peculiarity, when referred to wind-mills, which exclusively belongs to this contrivance.

An ingenious horizontal mill by Messrs. Claude François, and Jean Claude du Bost, is described in Recueil des Machines et Inventions approuvées par l'Acad. Roy. des Sciences, tom. vii. Some judicious remarks on the comparative advantages of Horizontal and Vertical Wind-mills, and indeed much useful information on the subject of Wind-mills in general, may be found in the second vol. of Dr. Brewster's edition of Ferguson's Lectures.

For M. Prony's expedient for equalizing the velocity and effects of wind-mills, see the article CONDENSER of Forces in this volume.

WIPERS, in some kinds of machinery, as oil-mills, powdermills, fulling-mills, are pieces projecting generally from horizontal axles, for the purpose of raising stampers, pounders, or heavy pistons, in vertical directions, and then leaving them to fall by their own weight.

When the wipers are only small cylinders projecting perpendicularly from the surface of the horizontal arbor, on which they are fixed, the force with which they elevate the respective stampers will not act uniformly during the whole time in which they are rising; yet, a uniformity of force and velocity is generally a desireable thing to be attained; and may always be effected by assigning a proper form to the wipers and communicating parts. A few directions for the determination of the due shape are here given, for the use of the mechanic.

Suppose that in fig. 15. pl. XXXII. the circle described about the centre a is a vertical section of the arbor on which the wipers are placed; and that the line ba shews the distance of an arm of one of the stampers from the centre a: describe with centre a and radius ab an arc bed... k, on which set off the equal parts bc, cd, de, ef, &c. as small as can conveniently be done: draw the radii ac, ad, ae, &c. on the extremities of which

erect perpendiculars equal to the respective arcs cb, db, eb, &c. and continue them until the last of them Nk is equal to the height to which the stamper is to be elevated: this being done, draw the curve No through the extremities of the several perpendiculars to the radii, it will form an involute of the circular are bk (which indeed may be either constructed thus or in the usual way at once, with a thread), and will be the figure that may be given to the upper surface of a wiper, when it is to give a uniform motion to the rising stamper. For as all the radii of curvature of No are tangents to the circumference of the generating circle bk, the arm mb of the stamper can never touch the wiper in more than one point (or horizontal line, whose section is a point). When it is the point 8, for example, the radius ad which answers to the tangent dd will be horizontal; of consequence dd will be perpendicular to the horizon, and its extremity alone will touch мb; dd at the same time will be the height to which the stamper will be raised. As the same thing will obtain at all the points where the arm мb touches the wiper, the arm of the lever which communicates the force will be constantly the same, that is, it will be equal to ab; and the arm of the lever at which the resistance acts being always equal to мb, it follows that the stampers will be raised entirely with a uniform force, and in a direction perpendicular to the horizon.

To determine the position of the point k, or the magnitude of the arc kb, the distance ab must be known, and the circumference c of the circle found corresponding to this radius: then make the line L equal to the height to which the stamper is to be raised; and say as c to L, so is 360° to the degrees and parts in the arc bk or the angle bak: draw from a the line bk, making with ba the angle thus found, and k is then ascertained. Divide the line L and the arc bk into an evenly even number of parts, set off from the points c, d, e, &c. of the arc the tangents in arithmetical progression, and equal to the respective parts on the line L measured from one of its extremities; and thus the curve Nob will be traced with great facility. The shape of the wipers as they are fixed singly in the arbor, will also appear from the same figure.

In the figure we have represented only one stamper and one wiper: but it often happens that 6, 8, 10, or more stampers are worked by wipers projecting from one horizontal arbor: in this case the wipers should be so distributed that the resistance arising from all the stampers shall be as nearly as possible a constant quantity: to effect this, let all the stampers be placed at equal distances in a line parallel to the axle or arbor; let also a single spiral run once completely round from one end of the arbor to the other, and let the wipers be at equidistant positions

on this spiral: thus will all the stampers be raised and permitted to fall at equidistant intervals during every rotation of the arbor.

Sometimes a small roller is fixed to the extremity of the arm mb, to diminish the friction; and in this case a curve must be drawn within Nb, parallel to it, and at a distance equal to the radius of the roller; this new curve exhibiting the shape and position of the upper face of the wiper.

In some machines stampers or pistons are raised by giving a proper curvature to the arm мb, and fixing the roller upon the extremity of a bent bar, whose end is in the direction of a radius produced in this case the arm must be shaped into part of a cycloid, the radius of whose generating circle is equal to the distance from the extremity of the wiper to the centre of the arbor; and this curve must be placed at the outer part of the rollers, to form the lower face of the arm.

The wiper may often be formed with great propriety like the Archimedean spiral, according to the method described by Dr. Brewster, and thus raise a stamper with a uniform motion. To this end let AH (fig. 12. pl. XXXII.) be a wheel put into motion by any power which is sufficient to raise the weight MN, by its extremity o, from o to e, in the same time that the wheel moves round one fourth of its circumference, it is required to fix upon its rim a wing OBCDEH which shall produce this effect with an uniform effort. Divide the quadrant on into any number of equal parts om, mn; &c. the more the better, and oe into the same number ob, bc, cd, &c. and through the points m, n, p, H, draw the indefinite lines AB, AC, AD, AE, and make AB equal to ab, ac to AC, AD to Ad, and AE to Ae; then through the points O, B, C, D, E, draw the curve OBCDE, which is a portion of the spiral of Archimedes, and will be the proper form for the wiper or wing OHE. It is evident that when the point m has arrived at o, the extremity of the frame will have arrived at b because AB is equal to ab; and for the same reason, when the points n, p, н, have successively arrived at o, the extremity of the frame will have arrived at the corresponding points c, d, c. The motion therefore will be uniform, because the space described by the weight is proportional to the space described by the moving power, ob being to oc, as om to on. If it be required to raise the weight MN with an accelerated or retarded motion, we have only to divide the line oe, according to the law of acceleration or retardation, and divide the curve OBCDE as before. It is scarcely necessary to add, that the vertical bar between N and м must be kept from lateral deviations, by being made either to run between rollers, or to slide in a groove.

We have all along supposed that the wheel or the arbor which carries the wipers, turns upon a horizontal axis: we might

exhibit methods by which stampers, &c. could be raised uniformly by wheels moving at right angles to the plane in which these stampers move; but such methods are intricate and not much to be recommended, as they may always be avoided by asmall addition of the machinery, or some slight modifications in its general distribution.

WORCESTER, Marquis of, his Century of Inventions. The curious and interesting tract, first published under this title about the middle of the seventeenth century, though often referred to by mechanical writers, being but little known, and containing various striking hints, some now matured, and others not yet completed; it is conceived its entire insertion in this place will be acceptable to the inquisitive reader.

1. Several sorts of seals, some shewing by screws, others by gages, fastening or unfastening all the marks at once: others by additional points and imaginary places, proportionable to ordinary escutcheons and seals at arms, each way palpably and punctually setting down (yet private from all others but the owner, and by his assent,) the day of the month, the day of the week, the month of the year, the year of our Lord, the names of the witnesses, and the individual place where any thing was sealed, though in ten thousand several places, together with the very number of lines contained in a contract, whereby falsification may be discovered, and manifestly proved, being upon good grounds suspected.

Upon any of these seals a man may keep accounts of receiptsand disbursements from one farthing to an hundred millious, punctually shewing each pound, shilling, penny, or farthing.

By these seals likewise any letter, though written but in English, may be read and understood in eight several languages, and in English itself to clean contrary and different sense, unknown to any but the correspondent, and not to be read or understood by him neither, if opened before it arrive unto him; so that neither threats, nor hopes of reward, can make him reveal the secret, the letter having been intercepted, and first opened by the enemy.

2. How ten thousand persons may use these seals to all and every of the processes aforesaid, and yet keep their secrets from any but whom they please.

3. A cipher and character so contrived, that one line, without returns and circumflexes, stand for each and every of the twenty-four letters; and as ready to be made for the one letter as the other.

4. This invention refined, and so abbreviated, that a point only sheweth distinctly and significantly any of the twenty-four