thers sessile, sitting on the tips of the petals; follicle round. There are four species. EMBRACERY, is an attempt to corrupt or influence a jury, or any way incline them to be more favourable to the one side than the other, by money, promises, letters, threats, or persuasions; whether the juror, on whom such attempt is made, give verdict or not, or whether the verdict given be true or false, which is punished by fine and imprisonment; and the juror taking money, perpetual infamy, imprisonment for a year, and forfeiture of tenfold the value.

EMBRASURE, in fortification, a hole or aperture in a parapet, through which the cannon are pointed to fire into the moat or field. Embrasures are generally twelve feet distant from one another, every one of them being from six to seven feet wide with out, and about three within: their height above the platform is three feet on that side towards the town, and a foot and a half on the other side towards the field; so that the muzzle may be sunk on occasion, and the piece brought to shoot low.

EMBROCATION, in surgery, an external kind of remedy, which consists in an irrigation of the part affected with some proper liquor, as oils, spirits, &c. by means of a woollen or linen cloth, or a spunge, dipped in the same. The use of embrocation is either to attenuate and dislodge something obstructed underneath the skin, to ease pains, or to irritate the part into more warmth and a quicker sense of feeling, The pumping used in natural baths is properly an embrocation.

EMBROIDERY, a work in gold, or silver, or silk thread, wrought by the needle upon cloth, stuff, or muslin, into various figures. In embroidering stuffs, the work is performed in a kind of loom, because the more the piece is stretched, the easier it is worked. As to muslin, they spread it upon a pattern ready designed; and sometimes, before it is stretched upon the pattern, it is starched to make it more easy to handle. Embroidery on the loom is less tedious than the other, in which, while they work flow. ers, all the threads of the muslin, both lengthwise and breadthwise, must be continually counted; but on the other hand, this last is much richer in points, and susceptible of greater variety. Cloths too much milled are scarce susceptible of this ornament, and in effect we seldom see them embroidered. The thinnest muslins are left for this purpose, and they are embroidered to the greatest perfection in Saxony; in

other parts of Europe, however, they embroider very prettily, and especially in France.

There are several kinds of embroidery, as, 1. Embroidery on the stamp, where the figures are raised and rounded, having cotton or parchment put under them to support them. 2. Low embroidery, where the gold and silver lie low upon the sketch, and are stitched with silk of the same colour. 3. Guimped embroidery: this is performed either in gold or silver; they first make a sketch upon the cloth, then put on cut vellum, and afterwards sew on the gold and silver with silk thread: in this kind of embroidery they often put gold and silver cord, tinsel, and spangles. 4. Embroidery on both sides; that which appears on both sides of the stuff. 5. Plain embroidery, where the figures are flat and even, without cords, spangles, or other ornaments.

EMBROIDERY, no foreign embroidery, on gold or silver brocade, is permitted to be imported into this kingdom on pain of being seized and burned, and a penalty of 100l. for each piece.

EMBRYO, in physiology, the first rudiments of an animal in the womb, before the several members are distinctly formed; after which period it is denominated a fœtus. See FŒTUS and MIDWIFERY.

EMBRYO, in botany. See CORCULUM.

Hitherto it has

EMERALD. This mineral comes chiefly from Peru; some specimens have been brought from Egypt. Dolomieu found it in the granite of Elba. been found only crystallized. The primitive form of its crystals is a regular six-sided prism; and the form of its integrant molecules is a triangular prism, whose sides are squares, and bases equilateral triangles. The most common variety of its crystals is the regular six-sided prism, sometimes with the edges of the prism, or of the bases, or the solid angles, or both wanting, and small faces in their place.

Crystals short; lateral planes smooth, terminal planes rough; colour emerald green of all intensities; internal lustre between 3 and 4; vitreous; fracture small, imperfect, conchoidal, with a concealed foliated fracture, and fourfold cleavage; fragments sharp-edged; transparency 4 to 2; causes double refraction; scratches quartz with difficulty. Specific gravity from 2.600 to 2.7755.

The fossil here described is the occidental emerald, and appears from antique gems to have beer known in the earlier ages, though

at present it comes to us only from South America. Vauquelin found it to contain of silex 64.5, argil 16, glucine 13, oxide of chrome 3.25, lime 1.6, and water 2. The oriental emerald is a green corundum, or resplendent lustre, superior in hardness to every stone but the diamond, and of the specific gravity of 4.

EMERSION, in astronomy, is when any planet that is eclipsed begins to emerge or get out of the shadow of the eclipsing body. It is also used when a star, before hidden by the sun as being too near him, begins to reappear or emerge ont of his rays.

EMERSON (WILLIAM), in biography, a late eminent mathematician, was born in June, 1701, at Hurworth, a village about three miles south of Darlington, on the borders of the county of Durham; at least it is certain that he resided here from his childhood. His father, Dudley Emerson, taught a school, and was tolerably proficient in mathematics; and, without his books and instructions, perhaps his son's genius, though eminently fitted for mathematical studies, might never have been unfolded. Beside his father's instructions, our author was assisted in the learned languages by a young clergyman, then curate of Hurworth, who was boarded at his father's house. In the early part of his life he attempted to teach a few scholars; but whether from his concise method, for he was not happy in explaining his ideas, or the warmth of his natural temper, he made no progress in his school; he therefore soon left it off, and, satisfied with a moderate competence left him by his parents, he devoted himself to a studious retirement, which he thus closely pursued, in the same place, through the course of a long life, being mostly very healthy, till towards the latter part of his days, when he was much afflicted with the stone. About the close of the year 1781, being sensible of his approaching dissolution, he disposed of his whole mathematical library to a bookseller at York; and on May the 20th, 1782, his lingering and painful disorder put an end to his life, at his native village, being nearly 81 years of age.

Mr. Emerson, in his person, was rather short, but strong and well made, with an open countenance and ruddy complexion, being of a healthy and hardy disposition; he was very singular in his behaviour, dress, and conversation; his manner and appearance were that of a rude and rather boorish countryman; he was of very plain

conversation, and seemingly rude, commonly mixing oaths in his sentences, though without any ill intention; he had strong good natural mental parts, and could discourse sensibly on any subject, but was always positive and impatient of contradiction; he spent his whole life in close study, and writing books, from the profits of which he redeemed his little patrimony from some original incumbrance; in his dress he was as singular as in every thing else; he possessed commonly but one suit of cloaths at a time, and those very old in their appearance; he seldom used a waistcoat; and his coat he wore open before, except the lower button; and his shirt quite the reverse of one in common use, the hind side turned foremost, to cover his breast, and buttoned close at the collar behind; he wore a kind of rusty coloured wig, without a crooked hair in it, which probably had never been tortured with a comb from the time of its being made; a hat he would make to last him the best part of a life-time, gradually lessening the flaps, bit by bit, as it lost its elasticity and hung down, till little or nothing but the crown remained.

He often walked up to London when he had any book to be published, revising sheet by sheet himself: trusting no eye but his own, was always a favourite maxim with him. In mechanical subjects, he always tried the propositions practically, making all the different parts himself on a small scale; so that his house was filled with all kinds of mechanical instruments, together or disjointed. He would frequently stand up to his middle in water while fishing, a diversion he was remarkably fond of. He used to study incessantly for some time, and then for relaxation take a ramble to any pot ale-house where he could get any body to drink with, and talk to. The late Mr. Montague was very kind to Mr. Emerson, and often visited him, being pleased with his conversation, and used frequently to come to him in the fields where he was working, and accompany him home, but could never persuade him to get into a carriage: on these occasions he would sometimes exclaim, "Damn your whim-wham! I had rather walk." He was a married man, and his wife used to spin on an oldfashioned wheel, of his own making, a drawing of which is given in his "Mechanics."

Mr. Emerson, from his strong, vigorous mind and close application, had acquired deep knowledge of all the branches of mathematics and physics, upon all parts of

which he wrote good treatises, though in a rough and unpolished style and manner. He was not remarkable, however, for genius or discoveries of his own, as his works hardly shew any traces of original invention. He was well skilled in the science of music, the theory of sounds, and the various scales both ancient and modern; but he was a very poor performer, though he could make and repair some instruments, and sometimes went about the country tuning harpsichords.

The following is the list of Mr. Emerson's works, all of them printed in 8vo., excepting his "Mechanics" and his "Increments," in 4to., and his "Navigation" in 12mo. 1. The Doctrine of Fluxions. 2. The Projection of the Sphere, Orthographic, Stereographic, and Gnomonical. 3. The Elements of Trignometry. 4. The Principles of Mechanics. 5. A Treatise of Navigation on the Sea. 6. A Treatise on Arithmetic. 7. A Treatise on Geometry. 8. A Treatise of Algebra, in two books. 9. The Method of Increments. 10. Arithmetic of Infinities, and the Conic Sections, with other Curve Lines. 11. Elements of Optics and Perspective. 12. Astronomy. 13. Mechanics, with Centripetal and Centrifugal Forces. 14. Mechanical Principles of Geography, Navigation, and Dialling. 15. Commentary on the Principia, with the Defence of Newton. 16. Tracts. 17. Miscellanies.

EMERY, a stone of the ruby family, of which three kinds are usually distinguished in commerce; the Spanish, red, and common emery. The first sort is found in the gold mines of Peru, and being judged a kind of marcasite of that rich metal, is prohibited to be export ed. The red emery is found in copper mines, and the little there is of it in England comes from Sweden and Denmark. The common emery is taken out of iron mines, and almost the only sort used in England; it is of a brownish colour, bordering a little on red, exceedingly hard, and in consequence difficult to pulverize. The English are the only people who have the art of reducing common emery into powder, and thus send it to their neighbours. Of the powder, the most subtile and impalpable is the best; as to the stone, it should be chosen of a high colour, and as free of the rock as possible.

The consumption of emery is very considerable among the armourers, cutlers, locksmiths, lapidaries, masons, and other mechanics; some of whom use it to polish and burnish iron and steel works; others, to

cut and scallop glass, marble, and precious

stones.

EMETIC, a medicine which induces vomiting.

EMETIC tartar, the old name for tartrite of antimony.

EMOLLIENTS. See PHARMACY. EMPETRUM, in botany, heath, a genus of the Dioecia Triandria class and order. Natural order of Ericæ, Jussieu. Essential character: male, calyx three-parted; corolla three-petalled; stamens long: female, calyx three-parted; corolla three-petalled; styles nine; berry nine-seeded. There are two species; viz. E. album, white-berried heath, and E. nigrum, black-berried heath, crow or crake berry. These are low shrubs, seldom propagated in gardens, unless for variety's sake. They are natives of wild mountains, where the soil is heathy and full of bogs.

EMPIS, in natural history, a genus of insects of the order Diptera. Generic character: mouth with an inflected sucker and proboscis; sucker with a single-valved sheath and three bristles; feelers short, filiform; antennæ setaceous. These minute insects live likewise by sucking out the blood and juices of other animals. There are about 30 species. One of the most common species is the E. livida, which is a brownish fly; the wings are transparent, with dark veins. They are observed in fields and gardens. E. borealis, is of a more slender form than the common window fly, and of a blackish colour, with large, broad, oval wings, of a brown colour, and rufous legs, varied with black.

EMPLASTRUM, in pharmacy, a composition for external use, generally spread upon leather, linen, or some other convenient thing before it is applied. See PHARMACY. The following is a recipe for making the Ladies' Court Plaster: "Dissolve five ounces of isinglass in a pint of water, and having ready a quantity of thin black sarsenet, stretched in a proper frame, apply the solution warm with a brush equally over the surface. This is to be repeated, after it is dry, two or three times." Some give it a coat of gum benzoin dissolved in alcohol; but this is injurious rather than beneficial.

EMPLEURUM, in botany, a genus of the Monoecia Tetrandria class and order. Natural order of Aggregate. Rutace, Jussieu. Essential character: male, calyx four-cleft; corolla none: female, calyx fourcleft, inferior; corolla none; stigma cylindric, placed on the lateral toothlet of the

ELL

LLIPSIS, in geometry, a curve line returning into itself, and produced from the section of a cone by a plane cutting both its sides, but not parallel to the base. See CONIC SECTIONS.

The easiest way of describing this curve, in plano, when the transverse and conjuaxes AB, ED, (Plate V. Miscell. fig. 1.) are given, is this: first take the points F,f, in the transverse axis A B, so that the distances C F, Cf, from the centre C, be each equal to /ACCD; or, that the lines FD, ƒD, be each equal to AC; then, having fixed two pins in the points F, f, which are called the foci of the ellipsis, take a thread equal in length to the transverse axis A B; and fastening its two ends, one to the pin F, and the other to f, with another pin M stretch the thread tight; then if this pin M be moved round till it returns to the place from whence it first set out, keeping the thread always extended so as to form the triangle F Mf, it will describe an ellipsis, whose axes are A B, D E.

The greater axis, AB, passing through the two foci Ff, is called the transverse axis; and the lesser one D E, is called the conjugate, or second axis : these two always bisect each other at right angles, and the eentre of the ellipsis is the point C, where they intersect. Any right line passing through the centre, and terminated by the curve of the ellipsis on each side, is called a diameter; and two diameters, which naturally bisect all the parallels to each other, bounded by the ellipsis, are called conjugate diameters. Any right line, not passing through the centre, but terminated by the ellipsis, and bisected by a diameter, is VOL. III.

1

called the ordináte, or ordinate-applicate' to that diameter; and a third proportional to two conjugate diameters, is called the latus rectum, or parameter of that diameter which is the first of the three proportionals.

The reason of the hame is this: let BA, ED, be any two conjugate diameters of an ellipsis (fig. 2, where they are the two axes) at the end A, of the diameter A B, raise the perpendicular A F, equal to the latus rectum, or parameter, being a third proportional to AB, ED, and draw the right line BF; then if any point P be taken in BA, and an ordinate PM be drawn, cutting BF in N, the rectangle under the absciss A P, and the line PN will be equal to the square of the ordinate P M, Hence drawing NO parallel to A B, it appears that this rectangle, or the square of the ordinate, is less than that under the absciss A P, and the parameter AF, by the rectangle under AP and OF, or NO and OF; on account of which deficiency, Apollonius first gave this curve the name of an ellipsis, from EXETY, to be deficient.

In every ellipsis, as A E B D, (fig. 2), the squares of the semi-ordinates MP, mp, are as the rectangles under the segments of the transverse axis APX PB, Apx p B, made by these ordinates respectively; which holds equally true of the circle, where the squares of the ordinates are equal to such rectangles, as being mean proportionals between the segments of the diameter. In the same manner, the ordinates to any diameter whatever, are as the rectangles under the segments of that diameter.

As to the other principal properties of

B