Whatever varieties may arise as to the internal structure of wind-mills, there are certain rules with regard to the position, shape, and magnitude of sails, which will bring them into the best state to receive the action of the wind, and to produce a full effect. M. Parent set his sails, or vanes, at an angle of 55° from the axis on which they project; and that would have certainly proved the best if no other object than the acquisition of a certain degree of velocity had been desirable; but we find that from 72° to 75° gives a greater power; consequently, in their general application, vanes standing at that angle, or within one or two degrees, more or less, are best calculated to produce a sufficient impetus for light breezes.

Mr. Smeaton made several experiments, which gave results proving the hypothesis just stated. He had vanes set at the following angles, and found it better to give an excess of retirement from, than an excess of exposure to, the wind.

Angle with Angle with the Plane
the axis.
of Motion.

72° .........18°

No.

1

were more powerful than parallelograms; the extreme or outer bar being one third the depth of the whip, or vane staff. Attempts were made to fill the whole space with sails; but it was evident that, for want of sufficient passage for the wind, the intention was not fulfilled: when more than 7ths of the area was spread with sail, there was an immense pressure, which caused much friction and imminent danger, while the velocity was rather diminished than augmented. Length of sail is a great object,,

so far as relates to the acquisition of power, but where an excess prevails, many injuries are sustained; notwithstanding the boom and guys, used in many places for the support of long arms.

As water-mills are, in general, stopped by shutting out the water, and thus debarring further influence of the power at pleasure; so wind mills are commonly stopped by a pinch, or pressure, on the axis bearing the vanes. Some are likewise acted upon by a weight which tends to retard the motion, and so slackens the rotation as to enable the pinch to have more effect. We have seen instances where the great axle could be cast off in an instant; so that, although the vanes might continue to go round, the interior movements were stopped. This is an excellent contrivance, and may often save a mill from being burnt, when by accident, or neglect, the stones have come in contact and produced collisive sparks. But in such case, it is obvious that a sufficient counter-check should be created to retard the motion of the vanes; else they would, from want of due opposition, move round with great rapidity, and produce other dangers no less imminent. This prevention is easily effected by causing the lever, which raises the main axle, to act against a stiffset wheel, capable of checking its progress. Some mills have a weathercock placed in the line with the axis, projecting several feet, and having sufficient surface to cause the cap to move round, so as always to keep the batt of the axle direct to the wind. This is an admirable expedient, inasmuch as it effectually answers the intention, and supersedes the necessity for the miller's constant attention to the wind; which, when variable, occasions considerable interruption to other avocations, and may, eventually, be attended both with loss of time and some damage.

Mr. John Bywater, of Nottingham, obtained a patent for clothing, or unclothing, the sails of wind-mills while in motion: his

contrivance was nothing more than causing them to roll up lengthwise, by means of small wheels, or ratchets, placed near the axis, and acted upon by it in its revolution.

MILLS, horizontal wind, have likewise been tried, but they are both troublesome to manage and deficient in power: on the other hand, they are far safer, and cheaper in their construction than the vertical kind. The simplest mode of constructing a windmill is with a spiral sail, passing round a centre pole, tapering towards the summit, and spreading to a great width at the base. This certainly has not very great powers, but acts with great uniformity, and requires no attendance, since it matters not from what quarter the wind blows. We consider this machine to be very well calculated for raising water from fens, &c. both on account of its cheapness and its safety, even in the most exposed situations. The pole, or axis, to which the sail is fastened all the way up, being perpendicular, and every part presented to the wind giving it a tendency to rotation, while the main part being below, insures a steady action, and that absence of violent friction which cannot be effected in a vertical mill, or in any machine where the greater part of the power is derived from the extremities of long arms, or vanes. See WINDMILL.

MILLS, horse and hand, are usually upon a small construction, rarely calculated to produce any considerable effect, and more appropriate to domestic purposes of inferior consideration. These machines, as their names imply, derive their action from animal force, which is unquestionably the dearest, most irregular, and least efficient, of all the powers hitherto applied to mechanism. In horse-mills, one, two, or more horses, or other cattle, are made either to draw, or push before them, levers, which project from a centre shaft, bearing the great horizontal wheel that gives motion to the more remote parts, and which act with more or less effect, according to the length of the levers, and the number of cattle employed. For threshing, drawing water, grinding, polishing, &c. such a power answers as a substitute where water is not at command. But, owing to the inequality of pace, and to the great propensity all animals have to lean towards the centre (in lieu of moving with freedom along the given circle of perambulation), all machines worked by cattle invariably become speedily deranged, and are encumbered with an excess of friction, Hand-mills labour under a similar inconve

nience; though such as are regulated by. fly-wheels, which occasion a great accumulation of force, and at the same time dispose to a degree of regularity in its action, are both more efficient and more durable. Of these we have numbers, such as chaff-cutting machines, grind-stones, &c; indeed, the mangle may be included among this class. In several countries the whole of the flour, meal, &c. used by the natives, are produced by means of hand-mills; our legislature, however, considering these as drawbacks on the livelihood of a very numerous class, has prohibited their use, under very heavy penalties. In many parts of Scotland the tenants are generally thirled, i. e. invariably obliged to send whatever corn they wish to grind to some particular mill; any deviation is actionable. This was at one time, perhaps, necessary, for the encouragement of millers, when they first introduced water machinery into that kingdom; at present it operates not only as an inconvenience, but, in many instances, as a hardship, amounting nearly to a prohibition. The evil, however, sometimes carries its own remedy, for the tenants sell their corn to the owner of some other neighbouring mill; and, when it is ground, buy the flour it produced: thus they evade the thirling, which binds only to the grinding of what they do not dispose of.

MILLS, bark, are most frequently worked by cattle, and perform their office by means either of large beams called beetles, which being lifted'in successive order fall into cavities wherein the bark, previously dressed in a proper manner, is placed, and pounds it to a sufficient degree of fineness to answer the tanner's purpose. Madder, and many other articles used in various trades, are also broken in the same manner. Paper is made from rags, which being dusted in sieves, &c. and soaked, are macerated in a mill, which tears the several fibres apart, and reduces the whole to a fine pulp.

MILLS, coffee and pepper, are too well known to require detail; we were not a little surprised to find the ordinary machinery of this class, when extended to a very large scale, obtain a patent for the grinding of bark.

MILLS, oil, are very simple in their construction; they being nearly the same as cyder-mills; consisting of troughs wherein the seed is broken by the passage of immense cylinders, or cones, of iron or stone, and afterwards put into presses for the purpose of forcing the oil from the residuum; which is sold, under the name of oil-cake, for the purpose of fatting cattle.

MILLS, copper and brass, are almost invariably worked by water, having large wheels that give immediate action to hammers of great weight, some being near three hundred weight; these beat out the large slabs and bricks of metal into various forms, such as kettles, coppers, boilers, &c. and roll out sheets for various purposes, but especially for coppering the bottoms of ships. This process is effected by passing the heated metal between two cast iron cylinders, of about a foot diameter, which, having contrary motions, draw it through a small interval left between them; and, by reducing the thickness, give greater surface to the sheet. In this manner the metal may be brought to any degree of thinness; the workmen bringing the cylinders nearer to each other, by means of screws at each end, every time a plate has been passed. The same mills have shears, worked by offsets from the counter-wheels, that cut the edges of the plates perfectly even, and are sufficiently forcible to divide lumps of copper, full an inch thick and six or seven in breadth, at one cut, the metal being previously brought to a red heat.

MILLS, silk, cotton, &c. require much delicacy in their construction; their principal movements depend on the same principles as those of the mills described in the plate; the more minute parts, such as the bobbins, &c. being moved by means of one or more leather straps passing them, in close contact, so as to occasion them to revolve with an astonishing degree of velocity.

MILLS, saw, though extremely simple in their parts, require the greatest care in their formation. The saws which are moved by cranks (much the same as those in use for pumps in water-works), must be set with most scrupulous exactness, else they will not only tear obliquely, and destroy much wood, but create such an accumulation of friction as must deteriorate the powers of the machine so as to approach to equilibrium. In most instances the timber is brought forward to the saw by means of a small toothed wheel, and an axle whereon the rope that pulls the timber is gradually coiled. See SAW-MILL.

MILLS, flax, are generally worked by cattle; their construction is simple; the essential parts being the hackle, which combs the flax; and the scutcher, which strikes it: both tend to clearing away the coarser and unequal fibres, and to prepare

the material for being spun either by hand. or by means of machinery.

We feel some surprise at the neglect shewn towards a very ingenious and useful invention in the department of mill-work; viz. the action of wheels, mutually, without the aid of cogs, or teeth. We have instances of wheels having been worked for nearly 30 years, simply by means of contact; the fellies (or circumference), being made of pieces of wood, having their grain, or fibres, all pointing to the centre. This produces a certain degree of roughness, exteriorly, which causes two wheels, thus formed, to bind sufficiently for the purposes of communicating rotation, where the stress is not excessive; and, even in that case, much may be effected by causing the wheels to bear very hard against each other, so as to excite friction to such an extent as may overcome the resistance of the weight, &c. We have seen a spinning machine consisting only of a vertical wheel (turned by a foot lathe), that had its perimeter armed with a band of stout buff-leather; which coming in contact with a number of bobbins, &c. caused all to move with great rapidity. Each bobbin was under the care of a little girl, who, by means of a slider, could either set it to work by approximation to the wheel, or liberate it from agency by withdrawing it from contact.

Having said thus much on the subject of mill-work, we beg leave to refer those of our readers who may be in search of abstruse knowledge, to Olinthus Gregory's work on the Theory of Mechanics; and to the excellent practical treatise of the late Mr. Smeaton, for a great variety of experiments not only in this, but in many other most important branches of mechanics; which the limits of our volumes do not permit us to enter upon in any other than a brief, summary, and popular manner,

MILL. Froin and after July 1, 1796, every miller shall have in his mill a true balance, with proper weights; and every miller, in whose mill shall be found no balance or weights, shall forfeit not exceed. ing 20s.

Every person may require the miller to weigh, in his presence, the corn before it shall be ground, also after it shall be ground; and if he refuse, he shall forfeit not exceeding 40s. Every miller shall, if required, deliver the whole produce of the corn, allowing for the waste in grinding and toll, when toll is hereinafter allowed to be taken, on pain to forfeit not exceeding 18. per bushel, and

colour.

plish flowers coming out from the side, on short peduncles; the principal stalk has many of those heads of flowers on the upper part, for more than a foot in length; this, as also the branches, is terminated by like heads of flowers; the leaves move but slowly when touched, but the foot-stalks fall, when they are pressed pretty hard. It is a native of Brasil. M. pudica, humble plant, has the roots composed of many hairy fibres, which mat closely together; from these come out several woody stalks, declining towards the ground, unless supported, they are armed with short recurved spines, having winged or pinnate leaves; flowers from the axils, on short peduncles, collected in small globular heads, of a yellow "Naturalists," says Dr. Darwin, " have not explained the immediate cause of the collapsing of the sensitive plant; the leaves meet and close in the night during the sleep of the plant, or when exposed to much cold in the day-time, in the same manner as when they are affected by external violence, folding their upper surfaces together, and in part over each other like scales or tiles, so as to expose as little of the upper surface as may be to the air; but do not, indeed, collapse quite so far; for when touched in the night during their sleep, they fall still further ; especially when touched on the foot-stalks between the stems and the leaflets, which seems to be their most sensitive or irritable part. Now as their situation after being exposed to external violence resembles their sleep, but with a greater degree of collapse, may it not be owing to a numbness or paralysis consequent to too violent irritation, like the faintings of animals from pain or fatigue? A sensitive plant being kept in a dark room till some hours after day break, its leaves and leaf-stalks were collapsed as in its most profound sleep, and on exposing it to the light, above twenty minutes passed before the plant was thoroughly awake, and had quite expanded itself. During the night the upper surfaces of the leaves are oppressed; this would seem to show that the office of this surface of the leaf was to expose the fluids of the plant to the light as well as to the air." Dr. Darwin has thus characterized these plants.

"Weak with nice sense, the chaste Mimosa stands,

From each rude touch withdraws her timid hands;

Oft as light clouds o'erpass the summer glade,

Alarm'd she trembles at the moving shade;

And feels alive through all her tender form,

The whisper'd murmurs of the gathering storm;

Shuts her sweet eyelids to approaching night,

And hails with freshen'd charms the rising light."

MIMULUS, in botany, Monkey flower, a genus of the Didynamia Angiospermia class and order. Natural order of Personatæ.

Scrophulariæ, Jussieu. Essential character: calyx four-toothed, prismatical; corolla, ringent; the upper lip folded back at the sides; capsule, two-celled, many seeded. There are four species, natives of

North and South America.

MIMUSOPS, in botany, a genus of the Octandria Monogynia class and order. Natural order of Holoraceæ. Sapotæ, Jussieu. Essential character: calyx fourleaved; petals four; nectary sixteen-leaved; drupe acuminate. There are three species, of which M. elengi is a middle sized tree, with entire smooth leaves; flowers axillary, on many simple peduncles; calyxes tomentose; berry superior, defended at the base by the permanent calyx, having an obsolete groove on one side, shagreened all over with very minute callous dots. It is a native of the East Indies, where it is much cultivated on account of its

fragrant flowers, which come out chiefly in the hot season.

MINA, in Grecian antiquity, a money of account, equal to an hundred drachms.

MIND. See PHILOSOPHY of the Mind.

MINE, in natural history, a place under ground, where metals, minerals, or even precious stones are dug up.

As, therefore, the matter dug out of mines is various, the mines themselves acquire various denominations, as gold-mines, silver-mines, copper-mines, iron-mines, diamond-mines, salt-mines, mines of antimony, of alum, &c.

Mines, then, in general, are veins or cavities within the earth, whose sides receding from, or approaching nearer to, each other, make them of unequal breadths in different places, sometimes forming larger spaces, which are called holes: they are filled with substances, which, whether me.