imperfect; but, after repeated alterations, he completed it in its present form, in 1758; and it now consists of an outer, or water-wheel, having an inner wheel, furnished with forty-eight cogs, and turning on the same axle. With this cog-wheel is connected a vertical trundle, or pinion, with seven notches; and the axle of which passes through a floor above the wheel; its upper pivot being secured in a beam six inches above the floor. At the height of three feet three inches from the latter, two straight pieces of squared wood (each being four feet in length) are inserted through the axle of the pinion, at right angles, so as to form four arms that are moved round horizontally. To the end of these arms are affixed four iron plates, each twenty inches in length, and eight inches in breadth at the extremity nearest to the arms, but tapering to a point at the opposite ends.

The horizontal fly, here described, constitutes four thrashers, and is inclosed in a cylindrical wooden box, that is three and a half feet high, and eight feet in diameter: on the top of this box is an opening eight inches in width, extending a foot and a half from the circumference to its centre, and through which the sheaves of corn descend; the latter being previously opened, and laid separately on a board provided with two ledges, gradually declining towards such port, or opening. Within the cylindrical box there is an inclined plane, along which the straw and grain fall into a wire-riddle two feet square, that is placed immediately beneath a hole of a similar size: the riddle is jerked at each revolution of the spindle, by means of a knob fixed on its side; and is thrust backward by a small spring that presses it in a contrary direction. Thus, the short straw, together with the grain and chaff, that pass through the wide riddle, fall instantly into an oblong straight riddle, one end of which is raised, and the other depressed, by a similar contrivance. And, as the riddle last-mentioned is not provided with a ledge at the lower end, the long chaff, which cannot pass through, drops thence to the ground, while the grain and smaller chaff descend into a pair of common barn-fanners, and are thus separated with great exactness. These fanners are moved by means of a rope, that runs in a shallow groove cut on the circumference of the cog-wheel. In the mean time, the straw collected in the lower part of the box over the wide riddle, and through an opening two feet and a half square, is drawn down to the ground with a rake, by the persons employed to form it into trusses.

In 1772 another thrashing-machine was invented by Mr. Alderton of Alnwick, and Mr. Smart of Wark, Northumberland. The operation was performed by rubbing: the sheaves

being carried round between an indented drum six feet in diameter, and numerous indented rollers, that were arranged round, and attached to, this drum by means of springs; so that during the revolution of the machinery, the corn was separated from the straw by constant friction against the flutings of the drum. But this contrivance was soon disused; as many grains were thus crushed between the rollers.

The next invention is that of Mr. Andrew Meikle, in 1785, who obtained a patent, which is now expired; we have therefore given a plate (XXXIV), representing in fig. 1. the plan of elevation; in fig. 2. the ground plan; and in fig. 3. the essential parts of the machinery, so as to convey a tolerably accurate idea of his principle.

A (fig. 1. and 2.) is a large horizontal spur-wheel, which has 276 cogs, and moves the pinion B, having fourteen teeth. The latter imparts motion to a crown-wheel, c, that is provided with eighty-four cogs, and moves a second pinion, D, which is furnished with sixteen teeth. This pinion D, turns the drum HIKL (fig. 1. 2. and 3.), being a hollow cylinder, three feet and a half in diameter, and placed horizontally: on its outside are fixed, by means of screw-bolts, four scutchers, or pieces of wood, one side of which is faced with a thin iron plate; and which are disposed at an equal distance from each other, and at right angles to the axis of the drum.

P (fig. 2. and 3.) is an inclined board, on which the sheaves are spread, and whence they are introduced between two fluted cast-iron rollers, G, G (fig. 3.), that are three and a half inches in diameter, and revolve about thirty-five times in one minute. These rollers being only three-fourths of an inch from the scutchers or leaves of the drum HIKL (fig. 1. and 2.), serve to keep the sheaves steady, while the scutchers a, b, c, d, (fig. 2. and 3.) move with considerable velocity, and thus separate the grain from the straw, while both are thrown on the concave rack м (fig. 2.), which lies horizontally with slender parallel ribs; so that the corn may pass through them into the subjacent hopper N (fig. 1. and 3.).

o (fig. 3.) is a riddle or harp, through which the corn drops into a pair of fanners, P (fig. 1. and 3.), and from these it is generally obtained in a state fit for the market.

ORTS is a rake, consisting of four leaves, or thin pieces of wood; at the extremity of each is placed a row of teeth, e, f, g, h, that are five inches long. This rake moves in the concave rack M, (fig. 2.), in a circular direction; while the teeth catch the straw that had been thrown by the scutchers a, b, c, d, into the rack, and remove it to the contiguous place, v.

w (fig. 1.) represents the horse's course, which is twenty-seven feet in diameter.

x (fig. 1. and 2.) is the pillar for supporting the beams on which the axle of the spur-wheel is fixed.

Y, Y, Y (fig. 1.), and Y, Y (fig. 2.) shew the spindles, the design of which is to move the two fluted rollers, the rake, and the fanners.

To the description now given we have only to add, that the drum has a covering of wood at a small distance above it, for the purpose of keeping the sheaves close to the scutchers.

The number of persons requisite for attending the mill when working is six: one person drives the horses; a second hands the sheaves to a third who unties them, while a fourth spreads them on the inclined boards, and presses them gently between the rollers: a fifth person is necessary to riddle the corn as it falls from the fanners, and a sixth to remove the straw.

This machine can be moved equally well by water, wind, or horses. Mr. Meikle has made such improvements on the windmill as to render it much more manageable and convenient than formerly; and we are informed many wind-mills are now erecting in different parts of the country. As to the comparative expense of these different machines, the erection of the horse-machine is least; but then the expense of employing horses must be taken into consideration. One of this kind may be erected for 707. A water-mill will cost 107. more, on account of the expense of the water-wheel. A wind-mill will cost from 2001. to 3007. sterling.

In thrashing-machines, however, cheapness should not be the only consideration. It often happens in machinery, that things apparently cheap are ultimately very dear. Thrashing of corn requires a strong power, which neither weak men nor slight machines are competent to. On this account, strong and durable machines are to be recommended as cheapest in the end; performing more work, in a better manner, and not needing frequent repairs.

Some other well-constructed thrashing-machines are described in Gray's Experienced Millwright, Bailey's Descriptions of Machines approved by the Society of Arts, in the Repertory of Arts and Manufactures, the 2d vol. of Dr. Brewster's Ferguson, and the 11th vol. of the Pantologia.

With respect to the quantity of corn which a machine will thrash in a given time, it is not easy to give any precise information; the most important we have yet met with is given by Mr. Fenwick, who found from numerous experiments that a power capable of raising a weight of 1000 pounds with a umform velocity of fifteen feet per minute, will thrash two bolls

(eight bushels) of wheat in an hour; and that a power sufficient to raise the same weight with a velocity of twenty-two feet per minute, will thrash three bolls of the same grain in an hour. From these facts, this gentlemen has computed the following table, which is applicable to machines that are driven either by water or horses.

The first four columns of the preceding table contain different quantities of impelling power, and the last two exhibit the number of bolls of wheat in Winchester measure, which such powers are capable of thrashing in an hour, or in a day. Six horses, for example, are capable of thrashing ten bolls of wheat in an hour, or ninety-five in the space of nine hours and a half, or a working day; and 680 gallons of water discharged into the buckets of an overshot water-wheel of 15 feet diameter during a minute, will thrash the same quantity of grain.

TIDE-MILLS, as their name imports, are such as employ for their first mover the flowing and ebbing tide, either in the sea or a river.

Mills of this kind have not often, we believe, been erected in England, though several of our rivers, and particularly the Thames, the Humber, and the Severn, in which the tide rises to a great height, furnish a very powerful mover to drive any kind of machinery, and would allow of tide-mills being very advantageously constructed upon their banks. The erection of

such mills is not to be recommended universally, as they are attended with a considerable original expense; besides that some of their parts will require frequent repairs: but in some places where coals are very dear they may, on the whole, be found less expensive than steam-engines to perform the same work, and may on that account be preferred even to them.

We have not been able to ascertain who was the first contriver of a tide-mill in this country, nor at what time one was first erected. The French have not been so negligent respecting the origin of this important invention as to let it drop into ob scurity; but have taken care to inform us that such mills were used in France early in the last century. Belidor mentions the name of the inventor, at the same time that he states some peculiar advantages of this species of machine. "L'on en attribue," says he, " la première invention à un nomme Perse, maître charpentier de Dunkerque, qui mérite assurément beaucoup d'éloge, n'y ayant point de gloire plus digne d'un bon citoyen, que celle de produire, quelqu' invention utile à la société. En effet, combien n'y a-t'il point de choses essentielles à la vie, dont on ne connoît le prix que quand on en est privé: les moulins en général sont dans ce cas-là. On doit sçavoir bon gré à ceux qui nous ont mis en état d'en construire par-tout: par exemple à Calais, comme il n'y serpente point de rivieres, on n'y a point fait jusqu'ici de moulins à eau, & ceux qui vont par le vent chômant un partie de l'année, il y a des tems où cette ville se trouve sans farine, & j'ai vu la garnison en 1730, obligeé de faire venir du pain de Saint-Omer, au lieu qu'en se servant du flux & reflux de la mer, on pourroit construire autant de moulins à eau que l'on voudroit: il y a d'autres villes dans le voisinage de la mer sujettes au même inconvénient, parce qu' apparement elles ignorent le moyen d'y remédier."

Mills to be worked by the rising and falling of the tide admit of great variety in the essential parts of their construction; but this variety may perhaps be reduced to four general heads, according to the manner of action of the water-wheel. 1. The water-wheel may turn one way when the tide rises, and the contrary when it falls. 2. The water-wheel may be made to turn always in one direction. 3. The water-wheel may fall and rise as the tide ebbs and flows. 4. The axle of the water-wheel may be so fixed as that it shall neither rise nor fall, though the rotatory motion shall be given to the wheel, while at one time it is only partly, at another completely, immersed in the fluid. In the mills we have examined, the first and third of these divisions have been usually exemplified in one machine; and the second and fourth may readily be united in another: we shall, therefore, speak of them under two divisions only.