Strong ties of iron should in all cases be secured to the front of the wall, passing through it, and being secured by plates and keys in the front, and extending backward to a considerable distance, and secured to a row of piling driven into the solid ground. These land-ties will also considerably assist the wall in resisting the forward pressure of the soil behind it. Imme

diately at the back of the wall a firm body of concrete, or, at least, well-puddled clay, should be introduced. Whichever of these is used as a backing, it should be consolidated as much as possible, and it will thus resist the admission of moisture behind the wall, which is indispensable to secure its permanent durability. The concrete should be cast in from a height above its intended position, and allowed to set before it is filled in; and if clay be substituted, it should be thoroughly well rammed in, and made as solid as possible. Wheal. The ancient Cornish called

a mine huel, which has been corrupted into wheal.

Wheel and Axle. This machine is so named by reason of its consisting of a wheel and cylinders, having a common axis with pivots fixed in its extremities, on which the whole may revolve. This very simple and useful contrivance, although usually designated a second mechanical power, requires the consideration of no other principles than those adduced for the lever; it is nothing but a lever, having the radius of the wheel for one arm, and that of the cylinder or axle for the other, the fulcrum being the common centre of both. This machine is also termed the 'Perpetual Lever;' for since the power and the resistance operate respectively at the circumference of a circle revolving about an axis, it is obvious that the rotation must maintain the continuity.

Wheels, in locomotive engines: the

well-known invention for obtaining a rolling progressive motion. They receive names corresponding to the part of the engine or tender they support; as leading, trailing, &c. Driving wheels vary in size from 4 feet 6 inches up to 10 feet diameter. Leading and trailing wheels vary from 3 feet up to 4 feet 6 inches in diameter. Tender wheels are usually about the same size as the leading and trailing wheels of the engines they are attached to. Wheel-cutting machine, a machine for cutting out the teeth of wheels. The most perfect machines for shaping the teeth of wheels are those invented by Mr. Lewis, of Manchester, which are adapted for cutting the teeth of spur, bevel, and worm wheels, of either metal¦ or wood. The principal working parts of these machines and the mode of action is as follows:

Two side frames have angular ridges from end to end, to fit into corresponding grooves in the bottom of a travelling frame: this frame can be adjusted by a screw moved by a hand-wheel at the back of the machine: at the front of the machine is a strong spindle, placed vertically, to carry the work which is fixed on the top of it, and at the lower part is a large worm-wheel moved by a screw, to which is, connected a train of three wheels: the sizes of the first and third wheels must be such that half a revolution of a handle, which falls into a notch after each half-revolution, shall turn the work so that any point in the pitch-line of it will move through a distance equal to the pitch. To the travelling frame a slide is attached by bolts and joints, in such manner that it may be fastened to act vertically, or at an angle in the direction either of the length or breadth of the machine. The cutter, and its wheels for diminishing the speed and pulley for communicating mo

tion to it, are carried by the slide. The cutter is a circular piece of steel notched like a saw, and shaped to fit the spaces between the teeth of the wheel, and is raised or lowered by a rack at the back of the slide, worked by a pinion and handle. The travelling frame and slide being adjusted to the work, and the suitable wheels arranged for turning it the given distance, the machine is set in motion and the revolving cutter pressed down upon the rim of the wheel by the handle and rack till the space has been cut; the cutter is then raised, and by giving half a revolution to the handle attached to the worm-wheel apparatus, the spindle and work are turned so that the latter is in proper position for the cutter to act again. For a spur-wheel the slide acts vertically, for a bevel-wheel it acts at the requisite angle in the direction of the length, and for a worm-wheel at an angle in the direction of the breadth of the machine.

Whim, a machine used for raising ores, &c., worked by horses, steam, or water

Whim-shaft, in mining, the shaft by which the stuff is drawn out of the mine by the horse or steam whim Whispering gallery, a curvilinear corridor or balcony within the cupola of St. Paul's cathedral, London, and in other ecclesiastical buildings

White Chalk is a well-known native carbonate of lime, used by the artist only as a crayon, or for tracing his designs; for which purpose it is sawed into lengths suited to the port-crayon. White crayons and tracing chalks, to be good, must work and cut free from grit. From this material both whiting and lime are prepared, and are the bases of many common pigments and colours used in distempering, paperstaining, &c.

Wicker-work, at an early date, was occasionally employed for the roof

ing, if not for the entire construction, of churches

Wicket, a small gate or door within, or a part of a massive or large door or gate for the passage of pedestrians

Willow wood is of many varieties: it is perhaps the softest and lightest of English woods; it is planed into chips, and used for many simple purposes

Wimple, a plaited linen cloth which

nuns wear about their necks; also a flag or streamer

Winch or Wince, in mining, the wheel and axle frequently used to draw water, &c. in a kibble by a rope Winch and Axle, a machine constituting a small windlass, and consisting of a cylinder of wood which is capable of turning on its axis between two upright posts of the same material, or between the ends of a cast-iron frame: a lever at one or at each extremity of the cylinder is attached to an iron axle passing through the latter at right angles to its direction, and is furnished with a handle, which is parallel to that axle. The name winch is given to a lever or handle of this kind, and the word is supposed to be derived from the verb guincher, signifying, in old French, to turn, or bend in a curvilinear manner. The machine is used to raise a weight vertically, or to draw an object towards it; for which purposes the object is connected with it by a rope or chain which continually passes over the curved surface of the cylinder as the latter is made to turn on its axis by a man acting at the handle. Since the cylinder revolves once while the handle, or the extremity of the lever to which it is attached, is made to describe the circumference of a circle, it is evident that the mechanical power of the machine is precisely that of the wheel and axle. When of a simple form, it is employed to raise water from a well, and earth or some other

material from the shaft of a small mine; and one of a complex nature is used, by means of a crane, to raise casks or heavy packages from the ground to the upper part of a building.

When great weights are to be raised, the machine is usually fixed in a frame of cast iron, which is rectangular on the plan, but its extremities or faces have the form of a triangle, or of the letter A. The axle of the cylinder is supported on a horizontal bar at the middle of each end of the frame, and to the cylinder is attached a toothed wheel which turns with it on the common axis: above this wheel, and parallel to the cylinder, is an iron axle which carries a pinion with teeth working in those of the wheel, and causing the latter to revolve, the pinion itself being turned by means of the lever and handle at one or at each extremity of the frame. A machine of this kind is called a crab; and when a weight is to be drawn horizontally or raised above the cylinder, the machine must of course be bolted to the floor or firmly fixed in the ground, in order to prevent it from being moved from its place. In such machines there is generally, at one extremity of the cylinder, a wheel having on its circumference teeth like those of a saw; and a click or catch, which turns freely on a pin, is attached by that pin to the side of the frame in such a manner that it may fall between the teeth. By this contrivance, if the handle should break, or the moving power be taken off while the weight is suspended in the air, the latter is prevented from descending.

Machines of this kind are occasionally constructed, which have the power of holding the weight in any part of its ascent or descent without a ratchet-wheel and catch. The only disadvantage attending the machine, when compared with

an ordinary winch or capstan, is, that requires a much greater quantity of rope to raise or move the object through any given distance. It was first proposed in Europe by Mr. George Eckhardt, but machines of a like kind have, it is said, long been in use in the East.

The winch is employed in the common jack, which is used to lift great weights, or to move them through small distances. The handle turns a pinion with teeth, which act on others at the circumference of a small wheel; and on the axle of this is a pinion with teeth, which work in those of a rack-rod. The axles of the wheel and pinions being let into the sides of a case of wood or iron, the revolution of the wheel produces a rectilinear motion of the rack; and one end of the case being fixed to the ground, or against an immoveable object, the extremity of the rack at the opposite end forces forward the body which is to be displaced. Sometimes, instead of a rack, the machine is furnished with a wheel whose axle is hollow, and cut in the form of a concave screw: within this screw is one of the convex kind, which by the revolution of the wheel and its axle is made to move in the direction of the latter, and thus to press before it the object which is to be removed. This machine has, however, considerable friction.

The force exerted by a man in turning a winch vertically, varies according to the position of the lever with respect to the horizon. When the lever, or that part which is perpendicular to the axle, is perpendicular to the ground, and the handle is at the highest or lowest part of the circle described by the end of the lever, the man either pushes the handle directly from him or pulls it directly towards him; and in each case he exerts power which is estimated at 27 o 30 pounds; but when the lever i

in a horizontal position, the man either throws a great portion of his weight on the handle to press it down, or he exerts his muscular force in a direct manner to pull it upwards; and the force exerted in these positions is estimated at 140 or 160 pounds. The force exerted must very evidently have different values between these quantities in other positions of the winch; and the practice is to cause two men to work at the same time to turn the machine, one being at each extremity of the axle of the cylinder. The levers of the two winches are placed at right angles to one another; consequently, when one man is pushing or pulling horizontally, the other is pressing or pulling vertically, and thus the operation of turning goes on with nearly uniform intensity; the first man working in the least favourable position when the other is working in that which is most so. Wind (instrument for measuring the force and velocity of): a fly (resembling that of a revolving ventilator, or the sails of a wind-mill) is fixed to the small end of the vane of a weather-cock, so as to be turned with its circular disc to the wind; and it consequently revolves by the action of the wind with a rapidity increasing as the force of the wind increases. The revolutions of the axis of this fly are converted by a train of toothed wheels and screws into a vertical motion, by which a pencil is carried downwards, touching the surface of a vertical cylinder, the cylinder having the axis of the weathercock for its axis. As the vertical rod on which the pencil slides is attached to the vane of the weathercock, the point of the compass from which the wind blows is recorded on the side of the cylinder on which the mark is made; while the quantity of the wind is represented by the extent of the descent of the pencil. Wind-beam, in ancient carpentry, a

cross-beam used in the principals of many ancient roofs, occupying the situation of the collar in modern king-post roofs

Winding, in ships, twisting on an uneven surface

Winding engines. In winding engines for drawing coals from a pit, where a given number of strokes are required in drawing a corf, the diameter of the roll at the first lift must be ascertained. In this case the engine is supposed to have flat ropes, such as are generally used, and which lie upon each other. To find the diameter of a rope-roll at the first lift, it is necessary to know the depth of the pit, the thickness of the rope, and the number of strokes which the engine is intended to make in drawing up a corf or curves; then, the thickness of the rope being known and the number of strokes, the thickness of the ropes upon the roll can be determined, let the diameter of the roll be what it may. Suppose the thickness of the rope to be 1 inch, and the number of strokes 10; then the radius of the roll is increased 10 inches, or the diameter is increased 20 inches, whatever that diameter may be. Windlass, in mechanics, a machine by which a rope or lace is wrapped round a cylinder: in navigation, a horizontal machine of strong timber, used in merchant ships for heaving up the anchor, instead of a capstan

Wind-mill, a mill which derives its

motive power from the impulse of the wind. The building containing the mill-work is usually lofty, and placed on elevated ground. The machinery consists of a shaft, upon one extremity of which arms radiate at right angles, similarly to the spokes of a wheel: upon these, vanes or sails are set at a small angle, (about 22°.) By this means the wind, blowing directly upon the area occupied by the vanes, acts obliquely upon the whole of