poisons, the poison of hydrophobia, &c. There are likewise substances which are innocent when taken into the stomach, but which prove deleterious when taken into the lungs, or when applied to an abraded surface. Thus carbonic acid gas is continually swallowed with fermented liquors, and thus the poison of the viper may be swallowed with impunity; whilst inspiring carbonic acid instantly destroys, and the poison of the viper inserted into the flesh produce formidable effects. Many substances also act as poisons when applied either externally or internally, as arsenic, lead, &c. When a deleterious substance produces its effects, not only in mankind, but in all other animals, it is distinguished by the term common poison, as arsenic, caustic, alkali, &c. whilst that which is poisonous to man only, or to brute animals, and often to one genus only, is said to be a relative poison; thus, aloes is said to be poisonous to dogs and wolves; the phellandrium aquaticum kills horses, whilst oxen devour it greedily and with impunity. It appears, then, that substances act as poisons only in regard to their dose, the part of the body they are applied to, and the subject on which their powers are exerted.

It is often of great importance to be able to discover, by certain chemical tests, copper and lead, particles of which frequently find their way into the stomach, either through inadvertencies, as by the employment of certain kitchen utensils made of these materials, or by fraud, as when acetate of lead (sugar of lead) is made use of to revive wines that have grown sour by long keeping. If copper be suspected in any liquor, its presence may be ascertained by adding to it a solution of pure ammonia, which will strike a beautiful blue colour. If the solution be very dilute, it may be concentrated by evaporation; and if it contain a great excess of acid, as in the liquor of pickles, so much alkali must be added as will be sufficient to saturate the acid.

Lead is affirmed by Dr. Lamb to exist in water that passes through leaden pipes, in such quantities as to be injurious to the human frame; this has however been much doubted; but it is well known that petty dealers in wine have occasionally recourse to the acetate of lead to revive bad wines. Lead may be discovered in water, by adding to a portion of it about half its bulk of water impregnated with sulphuretted hydrogen gas. If lead be present, it will be manifested by a dark

brown, or blackish tinge. For discover. ing the presence of lead in wine, a test is employed, called from the name of the inventor, Hahnemann's wine test. This is prepared, by putting together into a small phial sixteen grains of sulphuret of lime prepared in the dry way, and twenty grains of acidulous tartrite of potash (cream of tartar). The phial to be filled with water and well corked, and occasionally shaken for a few minutes. When the powder has subsided, decant the clear liquor, and preserve it in a well stopped bottle for use. The test, when newly prepared, discovers lead by a dark coloured precipitate. Lead may be likewise discovered by adding to the wine a solution of the sulphate of soda, which will throw down a precipitate. If a large quantity of the acetate of lead has been taken, as by a child, inadvertently, on account of its saccharine taste, an active emetic must first be given, and then the hydro-sulphuret of potash, or of ammonia, be taken; a solution of the common sulphuret will answer.

POLAR, in general, something relating to the poles of the world, or poles of the artificial globes: thus we meet with polar circles, polar dial, polar projection, &c.

POLARITY, the quality of a thing considered as having poles; but chiefly used in speaking of the magnet. See MAGNETISM.

POLE, in astronomy, one of the extremities of the axis, on which the sphere revolves. These two points, each ninety degrees distant from the equinoctial or equator, are by way of eminence called the poles of the world; and the extremities of the axis of the artificial globes, corresponding to these points in the heavens, are termed the poles thereof. See GLOBE.

POLE, in spherics, a point equally distant from every part of the circumference of a great circle of the sphere, as the centre is a plane figure; or it is a point of ninety degrees distant from the plane of a circle, and in a line, called the axis, passing perpendicularly through the centre. The zenith and nadir are the poles of the horizon; and the poles of the equator are the same with those of the sphere.

POLES of the ecliptic, are two points on the surface of the sphere, 23° 30′ distant from the poles of the world, and 90° distant from every part of the ecliptic.

POLES, in magnetics, are two points of a loadstone, corresponding to the poles

of the world; the one pointing to the north, the other to the south. See MAG

NETISM.

POLE, PERCH, Or Ron, in surveying, is a measure containing sixteen feet and a balf.

POLE, OF POLAR star, is a star of the second magnitude, the last in the tail of ursa minor. Its longitude Mr. Flamstead makes 24° 14′ 41′′; its latitude, 66° 4′ 11′′. The nearness of this star to the pole, whence it happens that it never sets, renders it of vast service in navigation, &c. for determining the meridian line, the elevation of the pole, and, consequently, the latitude of the place, &c. See LATITUDE.

POLEMONIUM, in botany, a genus of the Pentandria Monogynia class and order. Natural order of Campanacex. Polemonia, Jussieu. There are five species, chiefly natives of the Cape of Good Hope.

POLEMOSCOPE, in optics, a kind of reflecting perspective glass, invented by Hevelius, who commends it as useful in sieges, &c. for discovering what the enemy is doing, while the spectator lies hid behind an obstacle.

POLIANTHES, in botany, a genus of the Hexandria Monogynia class and order. Natural order of Coronariæ. Narcissi, Jussieu. Essential character; coroll funnel form, curved in, equal, filaments inserted into the jaws of the corolla; germ at the bottom of the corolla. There is but one species, viz. P. tuberosa, tuberose.

POLICY of assurance, is the deed or instrument by which a contract of assurance is effected. The premium paid for the risk must be inserted in the policy, and likewise the date. Policies for assurance against the risks of the sea are distinguished into valued and open policies; in the former the property is assured at prime cost, at the time of effecting the policy; in the latter, the value is not mentioned, but is left to be afterwards declared, or to be proved in the event of a claim.

POLISHER, or BURNISHER, among mechanics, an instrument for polishing and burnishing things proper to take a polish. The gilders use an iron-polisher to prepare their metals before gilding, and the bloodstone to give them the bright polish after gilding. The polisher used by the makers of spurs and bits, &c. is partly iron, partly steel, and partly wood; it consists of an iron-bar, with a wooden handle at one end, and a

hook at the other, to fasten it to another piece of wood held in the vice, while the operator is at work. In the middle of the bow, withinside, is what is properly called the polisher, being a triangular piece of steel, with a tail, whereby it is rivetted to the bow. The polishers, among cutlers, are a kind of wooden wheels made of walnut-tree, about an inch thick, and of a diameter at pleasure, which are turned round by the great wheel; upon these they smooth and polish their work with emery and putty. The polishers for glass consist of two pieces of wood; the one flat, covered with old hat, the other long and half round, fastened on the former, whose edge it exceeds on both sides by some inches, which serve the workmen to take hold of, and to work backwards and forwards by. The polishers, used by spectacle-makers, are pieces of wood a foot long, seven or eight inches broad, and an inch and a half thick, covered with old beaver-hat, whereon they polish the shell and horn-frames their spectacle glasses are to be set in.

POLISHING, in general, the operation of giving a gloss or lustre to certain substances, as metals, glass, marble, &c.

POLITICAL arithmetic, is the application of arithmetical calculation to political subjects, as the public revenues, number of people, extent and value of lands, taxes, trade, manufactures, &c. of any commonwealth. See STATISTICS.

POLITY, or POLICY, denotes the peculiar form and constitution of the government of any state or nation; or the laws, orders, and regulations, relating thereto.

Polity differs only from politics, as the theory from the practice of any art. See LAW, GOVERNMENT, &c.

Some divide polity into that which relates to the regulations respecting mer cantile affairs; and to those which concern the judiciary government of the citizens: some add other branches, viz. those relating to ecclesiastical and military affairs, &c.

POLL, a word used in ancient writings for the head: hence, to poll, is either to vote or to enter down the names of those persons who give in their votes at an election.

POLL money, a capitation or tax imposed by the authority of parliament on the head or person, either of all indifferently, or according to some known mark of distinction.

POLLEN, in botany, the fecundating or fertilizing dust contained within the anthers or tops of the stamina, and dis

persed on the pistil when ripe, for the purpose of impregnation. This dust is commonly of a yellow colour, and is very conspicuous in the tulip and lily. If this powder is examined by the microscope, it will be found to assume some determinate form, which often predominates, not only through the different species of one genus, but through all the genera of an order. Being triturated in the stomach of bees, by which great quantities are collected in the hairy brushes with which their legs are covered, is supposed to produce the wax. See WAX.

POLLIA, in botany, a genus of the Hexandria Monogynia class and order. Natural order of Junci, Jussieu. Essential character: corolla inferior, six-petalled; berry many-seeded. There is but one species, viz. P. japonica.

POLLICHIA, in botany, a genus of the Monandria Monogynia class and order. Natural order of Amaranthi, Jussieu. Essential character; calyx one leafed, fivetoothed; corolla five-petalled; seed solitary; receptacle producing succulent aggregate scales, sustaining the fruit. There is but one species, viz. P. campestris, whorled-leaved pollichia, a native of the Cape of Good Hope.

POLLUX, in astronomy, a fixed star of the second magnitude in the constellation gemini, or the twins. The same name is also given to the hindermost twin, or posterior part of the same constellation.

POLYADELPHIA, in botany, a class of plants, the eighteenth in order, whose stamina are connected together at their bases into several series. The plants of this class are subdivided into orders, according to the number of their stamina; thus the polyadelphia pentandria contain five stamina; and the polyadelphia icosandria and polyandria contain twenty or more stamina. There are but few genera included in this class. The chocolate-nut has five stamina, or rather five bundles of stamina; each filament has five anthers. Monsonia has fifteen stamina in five bundles. The citron, lemon, and orange, belonging to the genus citrus, have twenty stamina in several bundles. The St. John's wort have many stamina collected into five bundles.

POLYANDRIA, in botany, a class of plants, the thirteenth in order, with hermaphrodite flowers, and a large number of stamina in each; these always exceed the number of twelve, and grow on the receptacle of the future seeds. By this circumstance, chiefly, the class is distinguished from the ICOSANDRIA, which

see.

The most striking character is the situation of the stamina, which are inserted into the calyx or petals, or both. This is an unerring mark of distinction. This class is subdivided into seven orders, from the number of the styles; the poppy, water-lily, &c. have one style; the peony, two; lark-spur, three; tetracera, four; columbine, five; water-soldier, six; virgin's bower, tulip-tree, &c. have many.

POLYCARDIA, in botany, a genus of the Pentandria Monogynia class and order. Natural order of Dumosa. Rhamni, Jussieu. Essential character: petals fiverounded; stigma lobed; capsule fivecelled, five-valved; seeds arilled. There is only one species, viz. P. madagascarensis, a native of Madagascar, where it was found by Commerson.

POLYCARPON, in botany, a genus of the Triandria Trigynia class and order. Natural order of Caryophylile. Essential character: calyx five-leaved; petals five, ovate, very small; capsule one-celled, three valved; seeds very many. There is only one species, viz. P. tetraphyllum, four-leaved all-seed, a native of the South of Europe.

POLYCNEMUM, in botany, a genus of the Triandria Monogynia class and order. Natural order of Holoracex. Atriplices, Jussieu. Essential character: calyx threeleaved; petals five, calycine; seed one, almost naked. There are five species.

POLYGALA, in botany, milk-wort, a genus of the Diadelphia Octandria class and order. Natural order of Lomentaceæ. Pediculares, Jussieu. Essential character: calyx five-leaved, with two of the leaves shaped like wings, and coloured: legume obcordate, two-celled. There are forty-five species.

POLYGAMIA, in botany, a class of plants, the twenty-third in order, the characters of which are, that they have flowers of different structure; some having male flowers, others female ones, and others hermaphrodite.

A polygamous plant must have some of its flowers hermaphrodite. By this circumstance its connection is cut off with the plants of the classes monœcia, and diœcia; in the former of these the plants are androgenous, that is, bear male and female flowers on the same root; in the latter on different roots. 1. We have instances of hermaphrodite and male flowers in the same plant, in the white hellebore, &c.; also in several of the umbelliferous plants, as the carrot, coriander, chervil, &c. 2. Instances of hermaphrodite and male flowers on distinct

plants, may be given in the palmetto, ginseng, Indian date plum. 3. Herma. phrodite and female on the same plant, as in the pellitory and orack. 4. Her maphrodite and female on different plants, as in most species of the ash-tree.

POLYGAMY, a plurality of wives or husbands in the possession of one man or woman, at the same time.

POLYGLOTT, among divines and critics, chiefly denotes a Bible printed in several languages. In these editions of the Holy Scriptures, the text in each language is ranged in opposite columns. The first polyglott Bible was that of Cardinal Ximenes, printed in 1517, which contains the Hebrew text, the Chaldee Paraphrase on the Pentateuch, the Greek version of the LXX, and the ancient Latin version. After this, there were many others, as the Bible of Justiniani, Bishop of Nebio, in Hebrew, Chaldee, Greek, Latin, and Arabic; the Psalter, by John Potken, in Hebrew, Greek, Ethiopic, and Latin; Plantin's Polyglott Bible in Hebrew, Chaldee, Greek, and Latin, with the Syriac version of the New Testament; M. le Jay's Bible, in Hebrew, Samaritan, Chaldee, Greek, Syriac, Latin, and Arabic; Walton's Polyglott, which is a new edition of Le Jay's Polyglott, more correct, extensive, and perfect, with several new oriental versions, and a large collection of various readings, &c.

POLYGON, in geometry, a figure with many sides, or whose perimeter consists of more than four sides at least: such are the pentagon, hexagon, heptagon, &c.

Every polygon may be divided into as many triangles as it has sides; for if you assume a point, as a, (See Plate XII. Miscel. fig. 14.) any where within the polygon, and from thence draw lines to every angle, a b, a c, a d, &c. they shall make as many triangles as the figure has sides. Thus, if the polygon hath six sides (as in the figure above) the double of that is twelve, from whence take four, and there remains eight: I say that all the angles, b, c, d, e, f, g, of that polygon, taken together, are equal to eight right angles. For the polygon having six sides, is divided into six triangles; and the three angles of each by 1.32, Eucl. are equal to two right ones; so that all the angles together make twelve right ones; but each of these triangles hath one angle in the point, a, and by it they complete the space round the same point; and all the angles about a point are known to be equal to four right

ones, wherefore those four, taken from twelve, leave eight, the sum of the right angles of the hexagon. So it is plain the figure hath twice as many right angles as it hath sides, except four.

Every polygon, circumscribed about a circle, is equal to a rectangled-triangle, one of whose legs shall be the radius of the circle, and the other the perimeter (or sum of all the sides) of the polygon. Hence, every regular polygon is equal to a rectangled-triangle, one of whose legs is the perimeter of the polygon, and the other a perpendicular drawn from the centre to one of the sides of the polygon. And every polygon circumscribed about a circle is bigger than it; and every polygon inscribed is less than the circle, as is manifest, because the thing containing is always greater than the thing contained. The perimeter of every polygon circumscribed about a circle, is greater that the circumference of that circle, and the perimeter of every polygon inscribed is less. Hence, a circle is equal to a right-angled triangle, whose base is the circumference of the circle, and its height the radius of it.

For this triangle will be less than any polygon circumscribed, and greater than any inscribed; because the circumfer ence of the circle, which is the base of the triangle, is greater than the compass of any inscribed, therefore it will be equal to the circle. For, if this triangle be greater than any thing that is less than the circle, and less than any thing that is greater that the circle, it follows that it must be equal to the circle. This is called the quadrature, or squaring of the circle: that is, to find a right-lined figure equal to a circle, upon a supposition that the basis given is equal to the circumference of the circle; but actually to find a right line equal to the circumference of a circle is not yet discovered geome trically.

POLYGON, in fortification, denotes the figure of a town, or other fortress. The exterior or external polygon is bounded by lines drawn from the point of each bastion to the points of the adjacent bastions; and the interior polygon is formed by lines joining the centres of the bas

tions.

POLYGONS, problems concerning. 1. On a regular polygon to circumscribe a circle, or to circumscribe a regular polygon upon a circle; bisect two of the angles of the given polygon, A and B, (fig. 15.) by the right lines, A F, B F; and on the point F, where they meet with the

radius, A F, describe a circle, which will circumscribe the polygon. Next, to circumscribe a polygon divide 360 by the number of sides required. to find e F d; which set off from the centre, F, and draw the line, de, on which construct the polygon as in the following problem. 2. On a given line to describe any given regular polygon: find the angle of the polygon in the table, and in E set off an angle equal thereto: then drawing E A =ED through the points E, A, D, describe a circle, and in this applying the given right line as often as you can, the polygon will be described. 3. To find the sum of all the angles in any given regular polygon; multiply the number of sides by 180°; from the product subtract 360°, and the remainder is the sum required: thus in a pentagon, 180 × 5 =900, and 900-360-540, the sum of all the angles in a pentagon. 4. To find the area of a regular polygon: multiply one side of the polygon by half the number of sides; and then multiply this product by a perpendicular, let fall from the centre of the circumscribing circle, and the product will be the area required: thus, if A B (the side of a pentagon) 54 × 24 135, and 135 × 29

(the perpendicular) 3915 the area required. 5. To find the area of an irregular polygon, let it be resolved into triangles, and the sum of the areas of these will be the area of the polygon.

POLYGONAL numbers, are so called, because the units whereof they consist may be disposed in such a manner as to represent several regular polygons.

The side of a polygon number is the number of terms of the arithmetical progression that compose it; and the number of angles is that which shows how many angles that figure has, whence the polygonal number takes its name.

"To find any polygonal number proposed," having given its side, n, and angles, a. The polygonal number being evidently the sum of the arithmetical progression, whose number of terms is n and common difference a-2, and the sum of an arithmetical progression being equal to half the product of the extremes, by the number of terms, the extremes, being 1, and 1+d.

n−1=1+a -2.n-1; therefore, that number, or this sum, will be

POLYGONUM, in botany, a genus of Natural order of Holoracex. Polygoneæ. tho Octandria Trigynia class and order. Jussieu. Essential character: calyx none; corolla five-parted, calycine: seed one, angular. There are thirty-six species.

POLYGYNIA, among botanists, denotes an order or subdivision of a class of

plants, comprehending such plants of that class as have a great number of pistils, or female organs of generation.

POLYHEDRON, in geometry, denotes a body or solid comprehended under many sides, or planes. A gnomonic polyhedron is a stone with several faces, whereon are described various kinds of dials.

POLYHEDRON, polyscope, in optics, is a multiplying glass or lens, consisting of several plane surfaces disposed into a convex form.

POLYMNIA, in botany, a genus of the Syngenesia Polygamia Necessaria class and order. Natural order of Composite Oppositifolia. Corymbiferæ, Jussieu. Essential character: calyx exterior, four or five-leaved; interior ten-leaved; the leaflets concave; down none; receptacle chaffy. There are five species.

POLYNEMUS, the polyneme, in natural history, a genus of fishes of the order Abdominales. Generic character: head compressed, covered with scales; snout very obtuse and prominent: gill-membrane, five or seven-rayed; separate filaments near the base of the pectoral fins. Shaw enumerates ten species; Gmelin only four.