Description of a corn-mill.

the eye of the millstone, where it falls upon the top of the rynd, and is, by the motion of the rynd, and the leather under it, thrown below the upper stone, and ground between it and the lower one. The rapid motion of the stone, creates a centrifugal tendency in the corn going round with it, by which means it gets farther and farther from the centre, as in a spiral, in every revolution, until it is quite thrown out; and being then ground, it falls through a spout, called the mill-eye, into a trough placed for its reception.

When the mill is fed too fast, the corn bears up the stone, and is ground too coarse; besides the mill is apt to get clogged, and to go too slowly. When the corn is scantily supplied, the mill goes too fast, and the stones, by their collision, are apt to strike fire. Both these inconveniences are avoided, by turning the regulating pin S backward or forward, in order to draw up or let down the shoe, as the case is observed by the miller to require.

The heavier the running millstone, and the greater the quantity of water falling upon the wheel, the faster will the mill bear to be fed, and consequently the greater the performance of the mill and on the contrary, the lighter the stone, and the less the quantity of water, the slower must be the feeding. When the stone is considerably worn, and become light, its weight must either be increased by some artificial addition, or the mill must necessarily be fed slowly; otherwise the stone will be too much borne up by the corn under it, to grind the meal suffi ciently fine.

The power necessary to turn a heavy millstone, is but very little more than what is necessary to turn a light one; for as the stone is supported upon the spindle of the bridge-tree, and the end of the spindle that turns in the brass foot is but small, the difference arising from the weight produces only an inconsiderable action against the power or force of the water. Besides, a heavy stone affords the same advantage as a heavy fly, that is, it regulates the motion much better than a light one, from its not being liable to such great fluctuations of velocity.

The centrifugal force carrying the corn towards the circumference of the stones, it is obvious that it will be crushed when it comes to a place where the interval between the two millstones is less than its thickness; yet, as the upper millstone is supported on a point which it can never quit, it may not be considered equally obvious why it should produce a greater effect when it is heavy than when it is light; since, if it were equally distant from the nether millstone, it could only be capable of a limited impression. But as experience proves

Form of the acting faces of millstones.

that the difference actually occurs, it may be proper to state the cause. The spindle of the millstone being supported by a horizontal piece of timber, about nine or ten feet long, resting only on both its ends, the upper millstone, by the elasticity of this piece, is allowed a vertical motion, and plays up and down; by which movement, the heavier the stones are the more forcibly is the corn wedged in between them.

In order to cut and grind the corn, both the upper and under millstones have channels or furrows cut in them, proceeding obliquely from the centre to the circumference. These furrows, in the direction of their length, are cut slantwise on one side, and perpendicularly on the other, so that each of the ridges which they form has a sharp edge; and in the two stones, these edges pass one another like the edges of a pair of scissars, and so cut the corn, to make it grind the more easily, when it falls upon the furrows. The furrows are cut the same way in both stones, when they lie upon their backs, which makes them run crosswise to each other when the upper stone is inverted by turning its furrowed surface towards that of the lower; for, if the furrows of both stones laid the same way, part of the corn would be driven onward in the lower furrows, and come out from between the stones without being either ground or bruised.

The grinding surface of the under stone is a little convex from the edge to the centre, and that of the upper stone a little concave; and they are farthest from one another in the middle, but approach gradually nearer towards the edges. By this means the corn, at its first entrance between the stones, is only bruised; but as it goes farther on towards the circumference or edge, it is cut smaller and smaller, and at last finely ground, just before it comes out from between them.

When the ridges become blunt and the furrows shallow by wearing, the running stone must be taken up, and both of them may then be drest anew with a chisel and mallet. Every time the stone is taken up, there must be some tallow put round the spindle and upon the bush; this unguent will soon be melted by the beat the spindle acquires from its turning and rubbing against the bush, which it will prevent from taking fire.

The bush must embrace the spindle quite close, to prevent any shake in the motion, which would cause some parts of the stones to grate against each other, whilst the other parts of them would be two far asunder, and by that means spoil the meal. Hence, whenever the spindle has worn the bush, so as to begin to shake in it, the stone must be taken up, and a chisel driven into several parts of the bush; and when it is taken out,

American mode of raising ground corn to the top of the mill.

wooden wedges must be forced into the holes; by which means the bush will be made closely to embrace the spindle again all round. In doing this, great care must be taken to drive equal wedges into the bush on opposite sides of the spindle; otherwise it will be thrown out of the perpendicular, and so hinder the upper stone from being set parallel to the under one, which is absolutely necessary for making good work. When any accident of this kind occurs, the perpendicular position of the spindle must be restored, by adjusting the bridge-tree with proper wedges put between it and the brayer.

It often happens, that the rynd is a little wrenched in laying down the upper stone upon it, or is made to sink a little lower on one side of the spindle than on the other; and this will cause one edge of the upper stone to drag all round upon the lower, while the opposite edge will not touch. This is easily rectified, by raising the stone a little with a lever, and putting bits of paper, card, or thin chips, between the rynd and the stone.

We shall mention in this place a very useful and ingenious contrivance, adopted by the American millwrights for raising the ground corn to the cooling boxes or place, from which it is conveyed into the bolting-machine. They place a large screw horizontally in the box which receives the flour from the millstones. The thread or spiral line of the screw is composed of pieces of wood about two inches broad and three long, fixed into a wooden cylinder seven or eight feet in length, which forms the axis of the screw. When the screw is turned round this axis, it forces the meal from one end of the trough to the other, where it falls into another trough, from which it is raised to the top of the mill-house by means of elevators, a piece of machinery similar to the chain pump. These elevators consist of a chain of buckets, or concave vessels like large teacups, fixed at proper distances upon a leathern band, going round two wheels, one of which is placed at the top of the mill-house, and the other at the bottom, in the meal-trough. When the wheels are put in motion, the band revolves, and the buckets, dipping into the meal-trough, convey the meal to the upper story, where they discharge their contents. The band of buckets is inclosed in two square boxes, in order to keep them clean, and preserve them from injury. It is obvious how much more complete this contrivance is, than the mode adopted in this country, of putting the meal into sacks, and then rais ing it up by the common machinery for that purpose.

The mechanism of a horse with respect to draught.

OF WHEEL-CARRIAGES.

In considering this subject, it will be proper to advert to the formation of the animal by which wheel-carriages are put in motion. The horse is admirably calculated for draught, and the circumstances enabling him to draw to the greatest advantage are, to a certain extent, so well known to every one at all conversant with mechanics, that it is not less a cause of surprise than of regret, that his valuable properties should still continue to be so much abused as we find them to be. But information spreads slowly among the mass of the people, and it is long in reaching provincial wheel-wrights, among whom, as amongst other classes of men, there is a disposition to follow the practice of their forefathers, without inquiring whether they are right or wrong. Much as men are attached to their interest, too, they are often cruel in opposition to it; and cruelty can never bear the light of reason in her path. When the broad-wheel act was passed, a great outcry was raised against it by those whom it would have benefited, and who, instead of complying with it, perversely rendered its provisions nugatory, by bevelling their wheels. Thus, instead of relieving their horses, they adopted a practice tending to oppress them more than ever. With respect to the position of the line of traction, errors of equal moment are frequently committed, as a little attention will enable any one to perceive, who shall consider for a moment the form of the shoulders of a horse. It is evident (see fig. 9, pl. V.) that, at the place where the neck rises from the chest of the animal, the shoulder-blades form the resting place of his collar or harness into a slope, a b. This slope or inclination forms an angle with a perpendicular to the horizon, of about fourteen or fifteen degrees; and therefore the line of traction or draught should form the same angle with the horizon, because he will then pull perpendicularly to the shape of his shoulder, and all parts of that shoulder will be equally pressed by the collar. Besides, in overcoming obstacles, the advantage of this inclined direction is mechanically great; the following demonstration of it, taken from Walker's "System of Familiar Philosophy" has not perhaps been improved upon. Call a, fig. 10, pl. V. a wheel, b an obstacle, c the axle of the wheel, d the spoke which at present sustains the weight. A line drawn from the nearest part of the horizontal line of draught c k to the fulcrum or obstacle at e, will form the acting part of a lever ge; and another line e d being drawn from the fulcrum e to the nearest part of the spoke d, will form the resisting part of the same lever. Now as the acting and resisting arms of the lever are of equal lengths, the lever becomes

Advantages of an inclined line of draught.

a scale-beam, and a draught in the line g k must be equal to the weight of the wheel and all that it sustains, besides the friction; for if g e d be a crooked lever, a pull at g must be equal to all the weight supported by d. But when a horse draws agreeably to the shape of his shoulder, in the line i h, the acting part of the lever he is lengthened nearly one-fourth; so that if it would require a pull at g equal to four hundred weight, a power applied at h will draw the wheel over the obstacle b with three hundred weight. To those unacquainted with the principles of mechanics, this truth may be easily proved by an ordinary scale-beam. The horse himself, considered as a lever, has in this inclined draught a manifest advantage over his obstacles, in comparison of a horizontal draught, as may be seen by fig. 9. When the horse is yoked to a post, or has any great obstacle to overcome, he converts himself into a lever, making his hind feet the fulcrum, and the centre of gravity of his body to lean over it, at as great a distance as possible, by thrusting out his hind feet; by this means, acting both by his weight and muscular strength, and lengthening the acting part of the lever a b, he overcomes the difficulty more by his weight than by his muscular strength for the muscles of the fore legs act upon the bones to so great a mechanical disadvantage, that though he exerts them with all his might, they serve, in great efforts, for little more than props to the fore-part of his body. Hence we see the great use of heavy horses for draught. But the great mechanical use and advantage of the inclined line of draught may be more particularly seen, by calling the line a b the acting part of the lever, and the nearest approach from the fulcrum b to the inclined line of draught (that is, bc) the resisting part of the lever: compare this with the resisting part of a lever touching the horizontal line of draught, (that is, b d,) and it will be found nearly double; in consequence, agreeably to the known properties of the lever, a weight at g would require double the exertion in the horse to remove it, that the same weight would require were it placed at e.

From the above data, several important practical conclusions may be drawn ;-one is particularly important, that single-horse carts are preferable to teams, because in a team, all but the shaft horse must draw horizontally, and consequently in a manner inconsistent with their structure, and the established laws of mechanics. The small horses of the north of England draw more weight of actual goods than our largest waggon horses, and go longer stages. The small horses of Ireland, as a common load, draw fifteen hundred weight of goods, and travel farther in a day than our waggons, and over worse roads