pendulum, somewhat improved by Mr. Crosthwaite, watch and clockmaker, Dublin, we have the following description, "A and B (fig. 12), are two rods of steel forged out of the same bar, at the same time, of the same temper, and in every respect similar. On the top of B is formed a gibbet C; this rod is firmly supported by a steel bracket D, fixed on a large piece of marble E, firmly set into the wall F, and having liberty to move freely upwards between cross staples of brass, 1, 2, 3, 4, which touch only in a point in front and rear (the staples having been carefully formed for that purpose); to the other rod is firmly fixed by its centre the lens G; of twentyfour pounds weight, although it should in strictness be a little below it. This pendulum is suspended by a short steel spring on the gibbet at C: all which is entirely independent of the clock. To the back of the clock-plate, I, are firmly screwed two cheeks nearly cycloidal at K, exactly in a line with the centre of the verge L. The maintaining power is applied by a cylindrical steel-stud, in the usual way of regulators at M. Now, it is very evident, that any expansion or contraction that takes place in either of these exactly similar rods, is instantly counteracted by the other; whereas in all compensation pendulums composed of different materials, however just the calculation may seem to be, that can never be the case, as not only different metals, but also different bars of the same metal, that are not manufactured at the same time, and exactly in the same manner, are found by a good pyrometer to differ materially in their degrees of expansion and contraction, a very small change affecting one and not the other." The expansion or contraction of straight-grained fir-wood lengthwise, by change of temperature, is so small, that it is found to make very good pendulum rods. The wood called sapadillo is said to be still better. There is good reason to believe, that the previous baking, varnishing, gilding, or soaking of these woods in any melted matter, only tends to impair the property that renders them valuable. They should be simply rubbed on the outside with wax and a cloth. In pendulums of this construction the error is greatly diminished, but not taken away.

PENGUIN. See APTENODYTES. PENELOPE, in natural history, a genus of birds of the order Gallina. By Latham, they are mostly arranged under the genus Meleagris, or the Turkey. Their legs, how

ever, are without spurs. They inhabit principally South America, and particularly Brasil and Guiana. The P. cristata, or guan, is two feet six inches in length. P. cumanensis, or the yacou, is of the size of a hen turkey, and is found in Cayenne and Guiana. The Marail is found in flocks in Guiana, feeds on fruits, and roosts on trees. See Aves, Plate XI. fig. 5.

PENIS. See ANATOMY.

PENNANTIA in botany, so named in honour of Thomas Pennant, a genus of the Polygamia Dioecia, class and order. Essential character: calyx, none; corolla five petalled; stamens five: pericarpium, three sided, two-celled, with solitary subtriquetrous seeds. There is but one species, viz. P. corymbosa, a native of New Zealand.

PENNATULA, in natural history, seapen, a genus of the Vermes Zoophyta class and order; animal not affixed, of various shapes, supported by a bony part within, naked at the base, the upper part with generally lateral ramifications, furnished with rows of tubular denticles producing radiate polypes from each tube. There are about eighteen species, of which P. coccinea is described as: stem round, radiating, with papillous polype-bearing sides, and clavate at the top. It is found in the White Sea, is soft, red, an inch and a half high, and as thick as the little finger, wrinkled, with the papillæ disposed in rows. P.phosphorea has a fleshy stem, with a rough midrib, and imbricate ramification. It inhabits most seas, and emits a very strong phosphoric light in the dark; about four inches long, red, stem villous, with a lanceolate rough midrib, and nearly incumbent rays, the tubes pointing all one way. P. reniformis; stem round, vermicular, supporting a kidney-shaped leaf-like head, producing polypes on one surface. It inhabits South Carolina: body expanded, kidney-shaped, flat, rising from a short round stem, and covered on the upper surface with numerous tubular orifices, through which the polypes are obtruded at pleasure; the upper surface is of a rich purple, the under side brilliant, and sometimes yellowish.

PENNY, an ancient silver coin, which, though now little used, was the only one current among our Saxon ancestors. It was then equal to th part of a pound. In Etheldred's time the penny was the 20th part of the Troy ounce, hence the denomination penny-weight. Till the time of Edward the first, the penny was struck with a cross

so deeply sunk into it, that it might on occasion be easily broken, and parted into halves and quarters, hence the term halfpence, and farthings or four things. We have now copper pence, which are much used in the way of change. They are manufactured by Mr. Bolton, and are very handsome coins.

PENNY weight, a Troy-weight, containing twenty-four grains, each of which is equal in weight to a grain of wheat, gathered out of the middle of the ear, and well dried. PENSION, no person having a pension from the crown, during pleasure, or for any term of years, is capable of being elected a member of the House of Commons. To receive a pension from a foreign prince or state, without leave of the king, has been held to be criminal, because it may incline a man to prefer the interest of such foreign prince to that of his own country.

PENSIONER, in general, denotes a person who receives a pension, yearly salary,

or allowance. Hence,

The band of gentlemen-pensioners, the noblest sort of guard to the king's person, consists of forty gentlemen, who receive a yearly pension of one hundred pounds, This honourable band was first instituted by King Henry VIII, and their office is to attend the King's person, with their battleaxes, to and from his chapel-royal, and to receive him in the presence chamber, or coming out of his privy-lodgings: they are also to attend at all great solemnities, as coronations, St. George's feast, public audiences of embassadors, at the sovereign's going to parliament, &c.

They are each obliged to keep three double horses and a servant, and so are properly a troop of horse. They wait half at a time, quarterly; but on Christmas-day, Easter-day, Whitsunday, &c. and on extraordinary occasions, they are all obliged to give their attendance. They have likewise the honour to carry up the sovereign's dinner on the coronation-day, and St. George's feast; at which times, the King or Queen usually confer the honour of knighthood on two such gentlemen of the band as their captain presents. Their arms are gilt battle-axes; and their weapons, on horse-back, in time of war, are curassiersarms, with sword and pistols. Their standard, in time of war, is, argent, a cross gules. Their captain is always a nobleman, who has under him a lieutenant, a standardbearer, a clerk of the check, secretary, pay. master, and harbinger.

PENSTOCK, a sluice, or flood-gaté, serving to retain or let go, at pleasure, the water of a mill-pond, or the like.

PENTACHORD, an ancient musical instrument, with five strings, whence the

name.

PENTAGON, in geometry, a figure of five sides and five angles. If the five sides. be equal, the angles are so too, and the figure called a regular pentagon.

The most considerable property of a pentagon is, that one of its sides is equal in power to the sides of a hexagon and a decagon, inscribed in the same circle; that is, the square of the side of the pentagon is equal to the sum of the squares of the sides in the other two figures. The area of a pentagon, like that of any other polygon, may be obtained by resolving it into triangles. Pappus has also demonstrated that twelve regular pentagons contain more than twenty triangles inscribed in the same circle. The dodecahedron, which is the

fourth regular solid, consists of twelve pentagons. In fortification, pentagon denotes a fort with five bastions.

PENTAGRAPH, an instrument whereby designs of any kind may be copied in what proportion you please, without being skilled in drawing. (Plate Pentagraph, fig. 1), is a plan of a pentagraph, and (fig. 2 and 3), part of the same on a larger scale.

The pentagraph is made of brass, and consists of four levers ABDE, the two longest, A B, are jointed together at their ends, the other two, DE, are also jointed together at one of their ends, and to the levers A B at the others. In this manner the instrument always forms a parallelogram, a Aae Ee and a Be a De; f, g, and h, are three tubes upon the levers, two of which, f, g, slide along upon their respective levers, and can be fixed at any point by screws (one of these tubes is shewn se parately in fig. 3), any one of these tubes is adapted to receive either a fulcrum or fixed centre, round which the whole instrument turns a blunt point or tracer, to pass over the original design, which is to be copied; or a crayon to draw the figure, or copy of the original design; these three points must be always in one right line, and by the construction of the levers, if they are once set in a line, they will continue in it through any of its motions.

The proportion in which it will reduce any figure will be easily calculated from the same principles as the lever; that the mag