observed throughout the kingdom. By statute 35 George III. c. 102, the justices in quarter-sessions, in every county, are required to appoint persons to examine the weights and balances within their respective jurisdictions. These inspectors may seize and examine weights in shops, &c. and seize false weights and balances; and the offender, being convicted before one justice, shall be fined from five shilling to twenty shillings. Persons obstructing the inspectors, to forfeit from five shillings to forty shillings. Inspectors to be recompensed out of the county rate. Standard weights to be purchased by the sessions out of the county rate, and produced to all persons paying for the production thereof. Informations to be within one month.

WEINMANNIA, in botany, so named in honour of Joh. Wilh. Weinmann; a genus of the Octandria Digynia class and order. Natural order of Saxifrage, Jussieu. Essential character: calyx fourleaved; corolla four-petalled; capsule two-celled, two-beaked. There are six species.

WELDING. Welding is that intimate union produced between the surfaces of two piecies of malleable metal, when heated almost to fusion and hammered. This union is so strong, that when two bars of metal are properly welded, the place of junction is as strong, relatively to its thickness, as any other part of the bar. Only two of the old metals are capable of firm union by welding, namely, platina and iron; the same property be. longs to the newly discovered metals, po

tassium and sodaum.

WERNERITE, in mineralogy, is of a colour between yellow and green; it occurs crystallized; specific gravity is about 3.6. It intumesces before the blow-pipe, and melts into a whitish enamel. It is found in the iron mines in Sweden and Norway.

WESTRINGIA, in botany, so named in honour of John Peter Westring; a genus of the Didynamia Gymnospermia class and order. Natural order of Verticillata. La biatæ, Jussieu. Essential character: calyx half, five-cleft, five-sided; corolla reversed, with four segments, the longest erect, cloven; stamens distant, the two shorter, or lowest, abortive There is only one species, viz. W. rosmariniformis, a native of New South Wales, near Port Jackson. WHALE. See BALENA.

WHALE fishery. See FISHERY. WHARF, a space on the banks of a haven, creek, or hithe, provided for the

convenient loading and unloading of ves. sels upon. The fee paid for the landing of goods on a wharf, or for shipping them off, is called wharfage; and the person who has the direction and oversight of the wharf, receives wharfage, &c. is called the wharfinger.

WHEAT. See TRITICUM.

WHEEL. This is one of the six powers of mechanism; and, without doubt, contributes more than any of the other five to the general convenience of mankind, by the wonderful variety of purposes, from a mill to a watch, wherein it is employed. It is, our intention, however, in this place, to confine ourselves to the wheel as appertaining to vehicles in general, referring the readers to the article MILL work, WATCH work, CLOCK work, &c. for the application of such wheels as come within those branches of the arts

Of carriage wheels, in general, we shall then treat; observing, that any attempt to prove that a carriage is more easily drawn upon wheels than upon sledges, would be an affront to the understanding of the reader. But whether high, or low, wheels are fitted for the purpose, has been a subject of dispute, even among persons of skill. Reason and experience, however, seem perfectly to agree in this, that wheels, whose centres are on a level with the moving power, will be easiest drawn along a level plane; and that the higher a wheel is, the more easily will it get over the obstacles it may meet with, provided the moving power be not below the centre. It seems to follow, therefore, that carriages drawn by horses, or oxen,

should have wheels whose centres have the height of the draft line; that is, of the shoulders of the horses, or the yokes of the oxen. This is true, however, only in the case of a horizontal road; in going up hill the distance of the line of draught from the road is somewhat less; because, when a man, or any other animal, is standing upon the side of a slope, his height is inclined to that slope; or rather the slope is inclined towards him, where he stands perfectly perpendicular. This being the situation in which cattle labour most, it is necessary to proportion the draft, so as to render it as light as possible while drawing up hill, therefore, it is usual, and highly proper, so to proportion the height of the axle, especially in carts with two wheels, to the point of draught, that the line drawn from the centre of the wheel to that point should rise at an angle of about twelve or fourteen degrees; thus, when the horse is labouring up hill he will

come nearly to a level with the wheel's centre, and draw to the greatest advantage. This may serve as a general rule; but where local circumstances prevail of a different tendency, and also in particular cases, the height of the wheels must be suited to meet such. We reckon that ordinary work, and where the horses do not exceed the height of fifteen hands and a half, the wheels should be from four feet eight inches to five feet two. Yet the immense loads drawn in the coal carts at Glasgow, on wheels more than six feet high, and other instances of a like kind, prove that very great powers are gained by using high wheels; under due construction and application the difference of the wheel's weight does not prove any material drawback. In ascending, high wheels will be found to facilitate the draught in exact ratio with the squares of their diameters; but in descending they are liable to press in the same proportion. An admirable device was produced by Lord Somerville, for throwing the weight behind the centre in going down hill, by cocking the fore-part of the body of a cart; so that while the shaft may incline downwards, in proportion to the line of declivity, the bottom of the cart's body should remain horizontal; this construction is now common in Devonshire, Somersetshire, &c.

Wheels are commonly made with what is called a dish; that is, the spokes are set at an angle into the nave, or centrepiece; so that, when the interior end of the nave is placed on the ground, the wheel may appear to be dished, or hollow in the centre. Experience has shown, that when wheels have been made cylindrical and not with the conical hollow just described, so that the spokes stood at right angles with the centre of the axle, numberless inconveniences arose; the dirt taken up by the wheel used to fall in between the nave and the axle, so as to choke and wear it considerably. Such wheels also require to stand wider apart and demanded greater road way; besides, they were very apt to be wrenched when pressed by any exterior resistance, and the spokes were forced back in the mortises. According to the present plan of dishing wheels, usually to about four inches in five feet of diameter, the exterior resistances are avoided; the axle being so turned down at its ends, as to cause the lower spoke, which bears up the load, to stand perpendicularly under the centre; this occasioning the upper parts of the two wheels on the same an

gle to spread from each other; while the lower parts converge in the same proportion. Cylindrical wheels, that is, such as are not dished, would answer, provided the carriage were always on a perfectly horizontal plane; but they would subject the nave to be loaded with mud, and pinch the load when consisting of light articles rising above the body of the carriage.

The spokes should be set so far from the outer end of the nave, that a perpendicular from the sole to the under side of the axle may fall, between an inch and two inches, between the bushes. By this, the pressure will be somewhat greater on the outer than on the inward bush, when the wheels are on a level. This ought to be so; for the inner part of the axle arm being much bigger than the outer, it has more friction, therefore should have less pressure; besides, every sinking of the wheel, more than the other, causes it to pinch the inner bush. The best mode of placing spokes in the naves is, to mortise them in two rows, alternately; this does not weaken the centre so much as when all the spokes are in one row, or band, and gives a greater degree of resistance outwards. The tire, or iron binding of a wheel, must be so laid on, whether in one or more bands,as to form the frustrum of a cone; but in heavy waggons it is usual to make the middle of the tire rise considerably, so as to bear the whole weight on hard roads, whereby the carriage will move lighter than if the frustrum were rectilinear; this form likewise causes stones, &c. to slip aside; but in soft soils it is apt to occasion much sinking. The axle arm should be taper, in order that it may give the wheel rather a disposition to slide off; otherwise it would be apt to close inwardly, and create excessive friction; hence the necessity for good iron wasters exteriorly, and substantial linch-pins. There is a common practice of setting the wheels forward; that is, giving them a slight inclination towards each other, whereby they are perhaps an inch nearer at their front than at their backs; this is done to make the wheel run more even on its sole, or bearing part, and to prevent its gaping forward; but it is evidently a distortion which prevents the wheel from running exactly at right angles with the transverse section of the carriage. The nave of a heavy wheel, that is, for our ordinary cart for field purposes, need not be more than twelve or fourteen inches in length; if too short, the wheel will wabble, unless fitted very tight on the axle; while too

long a nave is apt to catch the dirt from the upper part, and to project too much beyond the outer face of the fellies; the above length is exclusive of the pan at the outer end.

The proportion of wheels must be estimated according to the purposes to which they are to be applied; thus waggons have in general large hind-wheels, while in timber carriages the four are usually of the same height, or nearly so; the London common stage carts have large wheels, while the drays used by brewers have very low ones The reason is obvious; waggons and carts load behind; but timber carriages and drays load at the sides; therefore, in such, large wheels, however much they might favour the draught, would be extremely inconvenient; indeed incompatible. Wheels, whatever their size, should be made of well-seasoned tough wood, perfectly free from blemish; the naves are generally of elm, the spokes of oak, and the fellies of elm or of ash: such are found to answer best for all carriages attached to the ordnance department; in which the following are considered as the regular standard heights.

All the horse-artillery carriages, limbers, and waggons; the heavy six-pound. ers, and long three-pounders, and their limbers; the carriage of a six-pounder battalion gun; of a light five and a half inch howitzer; and the hind-wheels of an ammunition waggon, five feet. The limber to a light six-pounder, and five and a half inch howitzer, the carriage of a medium twelve-pounder, four feet eight inches. The limber of the latter four feet six inches. A sling-cart, five feet eight inches. The fore-wheels of an ammunition waggon, four feet. A pontoon carriage has the fore-wheels three feet, and the hind ones five feet six inches. The carriage of an eight inch howitzer, five feet; the limber, four feet. A ball ammunition cart, five feet.

We are disposed to recommend these proportions to the consideration of readers concerned in the construction, or in the use of wheel carriages; they being the result of innumerable experiments, submitted to unequivocal proof under every variety of locality and of burthen. We think it necessary, at the same time, to observe, that a correspondent of the Agricultural Magazine, formerly published by Longman, Hurst, Rees, and Orme, of Paternoster-row, has, in the eleventh number of that work, given, what appears to be, an excellent rule for the

proportions of wheels in waggons. It would not be admissible for us to give the whole of the reasonings of that correspondent, as contained in various numbers; but from that which we have particularized, we have the pleasure to furnish the following extract; or, at least, the sense of it.

"If the fore-wheel be four feet four inches in height, and the line of traction (draught) be drawn at an elevation of twelve degrees from the centre of its axle, the point where that line cuts the circumference of the wheel in its front gives that height from the plane on which the carriage stands, that will determine the radius of the hinder-wheel. In this instance, the hind-wheel would have a radius of two feet nine inches, giving of course five feet six inches for its diameter."

A view of the plate given in that work not only will illustrate the above explanation, but will satisfy a person respecting the justness of the proportions above detailed; when tempered by the following cautions, we consider the instruction given to be admirable. "The fore-wheel ought to be as nearly level with the point of draught, that is, where the shaft is sus pended by the gear, as may be convenient; observing that an angle of twelve degrees is to be given, on account of the difference between the horse's height as he stands at rest, and the real altitude of the point of draught from the ground, when he is in a state of exertion. During great efforts, horses lose very considerably of their standard, and thus bring the shaft to nearly a parallel with the plane on which they move. Attention must be paid to keeping the wheel within such limits as may not trespass on other matters, often of more consequence even than ease of draught; loading, turning, weight, expense, &c. must always form a part of the calculation "

WHEEL work. Of all modes of communicating motion, the most extensively useful is the employment of wheel-work, which is capable of varying its direction and its velocity without any limit.

Wheels are sometimes turned by simple contact with each other; sometimes by the intervention of cords, straps, or chains, passing over them; and in these cases the minute protuberance of the surfaces, or whatever else may be the cause of friction, prevents their sliding on each other. Where a broad strap runs on a wheel, it is usually confined to its situation, not by causing the margin of the wheel to project, but, on the con

trary, by making the middle prominent ; the reason of this may be understood, by examining the manner in which a tight strap running on a cone would tend to run towards the thickest part. Sometimes also pins are fixed in the wheels, and admitted into perforations in the straps; a mode only practicable where the motion is slow and steady. A smooth motion may also be obtained, with considerable force, by forming the surfaces of the wheels into brushes of hair. More commonly, however, the circumferences of the contiguous wheels are formed into teeth, impelling each other, as with the extremities of so many levers, either exactly, or nearly, in the common direction of the circumferences; and sometimes an endless screw is substituted for one of the wheels. In forming the teeth of wheels, it is of consequence to determine the curvature which will procure an equable communication of motion, with the least possible friction. For the equable communication of motion two methods have been recommended; one, that the lower part of the face of each tooth should be a straight line in the direction of the radius, and the upper a portion of an epicycloid, that is, of a curve described by a point of a circle rolling on the wheel, of which the diameter must be half that of the opposite wheel; and in this case it is demonstrable, that the plane surface of each tooth will act on the curved surface of the opposite tooth, so as to produce an equable angular motion in both wheels; the other method is, to form all the surfaces into portions of the involutes of circles, or the curves described by a point of thread which has been wound round the wheel while it is uncoiled; and this method appears to answer the purpose in an easier and simpler manner than the former. It may be experimentally demonstrated, that equable motion is produced by the action of these curves on each other; if we cut two boards into forms terminated by them, divide the surfaces by lines into equal or proportional angular portions, and fix them on any two centres, we shall find, that as they revolve, whatever parts of the surfaces may be in contact, the corresponding lines will always meet each other.

an

Both these methods may be derived from the general principle, that the teeth of the one wheel must be of such a form, that their outline may be described by the revolution of a curve upon a given circle, while the outline of the teeth of VOL. XII.

means

the other wheel is described by the same curve revolving within the circle. It has been supposed by some of the best authors, that the epicycloidal tooth has also the advantage of completely avoiding friction; this is however by no true, and it is even impracticable to invent a form for the teeth of a wheel, which will enable them to act on other teeth without friction. In order to diminish it as much as possible, the teeth must be as small and as numerous as is consistent with strength and durability; for the effect of friction always increases with the distance of the point of contact from the line joining the centres of the wheels. In calculating the quantity of the friction, the velocity with which the parts slide over each other has generally been taken for its measure. This is a slight inaccuracy of conception, for it is certain, that the actual resistance is not at all increased by increasing the relative velocity; but the effect of that resistance, in retarding the motion of the wheels, may be shown, from the general laws of mechanics, to be proportional to the relative velocity thus ascertained. When it is possible to make one wheel act on teeth fixed in the concave surface of another, the friction may be thus diminished in the proportion of the difference of the diameters to their sum. If the face of the teeth, where they are in contact, is too much inclined to the radius, their mutual friction is not much affected, but a great pressure on their axis is produced; and this occasions a strain on the machinery, as well as an increase of the friction on the axis. If it is desired to produce a great angular velocity with the smallest possible quantity of wheel-work, the diameter of each wheel must be between three and four times as great as that of the pinion on which it acts. Where the pinion impels the wheel, it is sometimes made with three or four teeth only; but it is much better in general to have at least six or eight; and considering the additional labour of increasing the number of wheels, it may be advisable to allot more teeth to each of them than the number resulting from the calculation: so that we may allow thirty or forty teeth to a wheel acting on a pinion of six or eight. In works which do not require a great degree of strength, the wheels have sometimes a much greater number of teeth than this; and, on the other hand, an endless screw or a spiral acts as a pinion of one tooth, since it propels the wheel through the breadth of one tooth I i

only into each revolution. For a pinion of six teeth, it would be better to have a wheel of thirty-five or thirty-seven than thirty-six; for each tooth of the wheel would thus act in turn upon each tooth of the pinion, and the work would be more equally worn than if the same teeth continued to meet in each revolution. The teeth of the pinion should also be somewhat stronger than those of the wheel, in order to support the more frequent recurrence of friction. It has been proposed, for the coarser kinds of wheelwork, to divide the distance between the middle points of two adjoining teeth into thirty parts, and to allot sixteen to the tooth of the pinion, and thirteen to that of the wheel, allowing one for freedom of motion.

The wheel and pinion may either be situated in the same plane, both being commonly of the kind denominated spurwheels, or their planes may form an angle; in this case one of them may be a crown or contrate wheel; or both of them may be bevelled, the teeth being cut obliquely. According to the relative magnitude of the wheels, the angle of the bevel must be different, so that the velocities of the wheels may be in the same proportion at both ends of their oblique faces; for this purpose, the faces of all the teeth must be directed to the point where the axes would meet. In cases where a motion not quite equable is required, as it sometimes happens in the construction of clocks, but more frequently in orreries, the wheels may either be divided a little unequally, or the axis may be placed a little out of the centre; and these eccentric wheels may either act on other eccentric wheels, or, if they are made as contrate wheels, upon a lengthened pinion. An arrangement is sometimes made for separating wheels which are intended to turn each other, and for replacing them at pleasure; the wheels are said to be thrown by these operations out of gear and into gear again. When a wheel revolves round another, and is so fixed as to remain nearly in a parallel direction, and to cause the central wheel to turn round its axis, the apparatus is called a sun and planet wheel. In this case, the circumference of the central wheel moves as fast as that of the revolving wheel, each point of which describes a circle equal in diameter to the distance of the centre of the two wheels; consequently, when the wheels are equal, the central wheel makes two revolutions, every time that the exterior

wheel travels round it. If the central wheel be fixed, and the exterior wheel be caused to turn on its own centre during its rovolution, by the effect of the contact of the teeth, it will make in every revolution one turn more, with respect to the surrounding objects, than it would make if its centre were at rest, during one turn of the wheel which is fixed; and this circumstance must be recollected when such wheels are employed in planetariums.

Wheels are usually made of wood, of iron, either cast or wrought, of steel, or of brass. The teeth of wheels of metal are generally cut by means of a machine; the wheel is fixed on an axis, which also carries a plate furnished with a variety of circles, divided into different numbers of equal parts, marked by small excavations; these are brought in succession under the point of a spring, which holds the axis firm, while the intervals between the teeth are expeditiously cut out by a revolving saw of steel. The teeth are afterwards finished by a file; and a machine has also been invented for holding and working the file. It is frequently necessary in machinery to protract the time of application of a given force, or to reserve a part of it for future use. This

is generally effected by suffering a weight to descend, which has been previously raised, or a spring to unbend itself from a state of forcible flexure, as is exemplified in the weights and springs of clocks and watches. The common kitchen jack is also employed for protracting and equalizing the operation of a weight; in the patent jack the same effect is produced by an alternate motion, the axis being impelled backwards and forwards, as in clocks and watches, by means of an escapement, and the place of a balance spring being supplied by the twisting and untwisting of a cord.

In these machines, as well as in many others of greater magnitude, the fly wheel is a very important part, its velocity being increased by the operation of any part of the force which happens to be superfluous, and its rotatory power serving to continue the motion when the force is diminished or withdrawn. Thus, when a man turns a winch, he can exert twice as much force in some positions as in others, and a fly enables him in some cases to do nearly one-third more work. In the pile engine, also, without the help of the fly, the horses would fall for want of a counterpoise, as soon as the weight is disengaged. Such a fly ought