lower end of the bar rests upon a fixed point, the bar will be expanded upwards, and raise the upper end of the pendulum just as much as its length was increased; and hence its length below the plates will be the same as before. Of this pendulum, somewhat improved by Mr. Crosthwaite, watch and clockmaker, Dub. lin, 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 twenty-four 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 clockplate, 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 diminisired, 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, however, are without spurs. They inhabit principally South America, and particularly Brazil 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 roots of 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 spe cies, 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 pa pillæ 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.

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 magnitude of the figures described by either of the points will be in the same proportion to each other, as the distances of those points from the fulcrum; thus if the point ƒ be the fulcrum, and if the distance from f to g be half the distance from fto h, the size of the figure described by the point g will be half the size of the figure described at the same time by the point h. The fulcrum, as we have said before, can be changed, as also the pencil and the tracer, and any of the three can be applied to either of the tubes upon the levers; if the tracer is placed in the tube h, the pencil in g, and the fulcrum at f, any figure described by the tracer h, will be exactly copied one half the size by the pencil at g, and if on the contrary the pencil is placed at h, and the tracer at g, the figure drawn by the pencil will be twice the size of the original tracer at g. When the fulcrum is placed between the two points at g, the figures described by each point will be inverted with respect to each other, though the same principle applies, that the magnitude of the figures will bear the same proportion to each other, as the distances of their tracing point from the fulcrum bear to each other. The last position of the instrument is seldom used, on account of the figure being inverted except when the figures traced and copied are equal to each other, or nearly so, as the first position will not allow of that.

:

It will be easily seen that by the sliding motion of the tubes g and f, the proportion between the three may be varied in any degree, and for this purpose the levers are engraved, and divisions made to set these tubes by, so as to reduce it in any proportion, and at the same time put the three points in the same right line, other. wise the figures will be strangely distorted; n n n is a silk thread, which the operator hooks round his fore finger; by pull ing this he raises up the crayon, g, so that it will not mark; each joint of the instrument is formed by a short axis, i, (fig. 2.) made fast, and moving with one lever, k; it has pivots at its ends, working in a small cock, l, screwed to the upper side of the

other lever beneath each joint a small tube, m, is screwed, its upper end receives the lower pivot of the axis i, and in the lower part a small spindle, n, is fitted, which has a castor at the bottom to support the weight of the instrument; by the turning of the spindle n, the castor will run in any direction. One of these castors is also fixed at the outer end of the levers, A and B, as well as beneath each joint. Care should be taken that the table, upon which the instrument is used, is a perfect plane, otherwise errors will arise from the tracer or crayon being sometimes thrown out of the perpendicular, and it is for the same reason that the levers are jointed with an axis, as explained before.

Fig. 4, Plate Pentagraph, is the common parallel ruler; A B are two rulers connected by two bars C D, which are of equal lengths, and the distance between the pins by which the levers C D are fixed to the rulers are the same distance from each other in both rulers; by this means it is easily seen, that the two rulers, A B, will always move parallel to each other.

Fig. 5. is another ruler differing from the other in being double; the advantage of it over fig. 4. is, that the two rulers A B can be moved parallel to each other without sliding endways, as the other does, every part of the moving ruler describing the arc of a circle.

PENTAMETER, in ancient poetry, a kind of verse, consisting of five feet, or metres; whence the name. The two first feet may be either dactyls or spondees, at pleasure; the third is always a spondee, and the two last anapests: such is the following verse of Ovid.

A pentameter verse, subjoined to an hexameter, constitutes what is called elegiac.

PENTANDRIA, in botany, the name of the fifth class of plants in the Linnæan system, consisting of plants which have hermaphrodite flowers with five stamina. There are six orders in this class, founded upon the number of styles.

PENTAPETES, in botany, a genus of the Monadelphia Dodecandria class and order. Natural order of Columniferæ. Malvacea, Jussieu. Essential character: calyx double, outer three-leaved; inner five-parted; stamina fifteen, with five ligules, petal-shaped; capsule five-celled, many-seeded. There is but one species,

viz. P. phonicea, scarlet-flowered pentapetes, a native of the East Indies and Japan.

PENTHORUM, in botany, a genus of the Decandria Pentagynia class and order. Natural order of Succulentæ. Sempervivæ, Jussieu. Essential character: calyx five or ten cleft; petals none, or five: capsule five-cusped, five-celled. There is only one species, viz. P. sedoides, American penthorum.

PENTSTEMON, in botany, a genus of the Didynamia Angiospermia class and order. Natural order of Personatæ. Essential character: calyx five-leaved; corolla bilabiate, ventricose; rudiment of a fifth stamen bearded above; capsule twocelled. There are two species, viz. P. lævigata, smooth pentstemon, and P. pubescens, hairy pentstemon

PENULTIMA, or penultimate syllable, in grammar, denotes the last syllable but one of a word; and hence the anti-penultimate syllable is the last but two, or that immediately before the penultima.

PENUMBRA, in astronomy, a partial shade observed between the perfect shadow and the full light, in an eclipse. It arises from the magnitude of the sun's body; for were he only a luminous point, the shadow would be all perfect; but by reason of the diameter of the sun, it hap. pens that a place which is not illuminated by the whole body of the sun does yet receive rays from a part thereof. See ASTRONOMY.

PEPLIS, in botany, purslane, a genus of the Hexandria Monogynia class and order. Natural order of Calycanthemæ. Salicaria, Jussieu. Essential character: calyx bell-shaped, with a twelve-cleft mouth; petals six, inserted into the calyx; capsule two-celled. There are two species, viz. P. portula, water purslane, and P. tetrandria.

PEPPER, in natural history, an aromatic berry, of a hot, dry quality, chiefly used in seasoning. See PIPER.

We have three kinds of pepper at this time in use in the shops; the black, the white, and the long pepper.

Black pepper is the fruit of a plant of the Diandria Trigynia class, without any flower petals; the fruit itself is roundish and rugose, and disposed in clusters: it is brought from the Dutch settlements in the East Indies.

The common white pepper is factitious, being prepared from the black in the following manner: they steep this in seawater, exposed to the heat of the sun for several days, till the rind or outer bark

loosens; they then take it out, and when it is half dry, rub it till the rind falls off; then they dry the white fruit, and the remains of the rind blow away like chaff. A great deal of the heat of the pepper is taken off by this process; so that the white kind is fitter for many purposes than the black. However, there is a sort of native white pepper, produced on a species of the same plant, which is much better than the factitious, and indeed little inferior to the black.

The long pepper is a dried fruit, of an inch, or an inch and a half in length, and about the thickness of a large goose quill: it is of a brownish-grey colour, cylindrical in figure, and said to be produced on a plant of the same genus.

Pepper is principally used by us in food, to assist digestion; but the people in the East Indies esteem it as a stomachic, and drink a strong infusion of it in water, by way of giving them an appetite: they have also a way of making a fiery spirit of fermented fresh pepper with water, which they use for the same purpose. They have also a way of preserving the common and long pepper in vinegar, and eating them afterwards at meals.

PEPPER water, a liquor prepared in the following manner, for microscopical observations: put common black pepper, grossly powdered, into an open vessel, so as to cover the bottom of it half an inch thick, and put to it rain or river water, till it covers it an inch; shake or stir the whole well together at the first mixing, but never disturb it afterwards: let the vessel be exposed to the air uncovered; and in a few days there will be seen a pellicle or thin skin swimming on the surface of the liquor, looking of several colours.

This is a congeries of multitudes of small animals; and being examined by the microscope, will be seen all in motion: the animals, at first sight, are so small as not to be distinguishable, unless to the greatest magnifiers; but they grow daily till they arrive at their full size. Their numbers are also continually increasing, till the whole surface of the liquor is full of them, to a considerable depth. When disturbed, they will sometimes all dart down to the bottom, but they soon after come up to the surface again. The skin appears soonest in warm weather, and the animals grow the quickest; but in the severest cold it will succeed, unless the water freezes.

About the quantity of a pin's head of this scum, taken up on the nib of a new pen, or the tip of a hair pencil, is to be

laid on a plate of clear glass; and if ap plied first to the third magnifier, then to the second, and finally to the first, will show the different animalcules it contains, of several kinds and shapes, as well as sizes.

PEPPERMINT, a species of mint. See

MENTHA.

PERAMBULATOR, a machine for measuring distances upon the ground. Its external figure is shewn in figs. 1. and

2. Plate Perambulator. A B is a maho

gany wheel, strongly framed and hooped with iron, that it may not wear; it turns in a handle, D E, which the operator holds in his hand, and thus wheels it along upon the ground. At F is a piece of mechanism to register the number of revolutions the wheel has made. The pivots of the wheel work into pieces of brass let into the two arms of the handle, DE; on the end of one of its pivots, a small pinion, a, (fig. 3.) is fixed; this turns another pinion, b, upon a long spindle, d, which conveys the motion to the machinery at F (fig. 2.); both pinions have eight teeth, therefore the spindle, d, turns in the same time as the great wheel, A B. This spindle is let into the wood-work of the handle, as is shewn in the dotted line, d, (fig. 2.) and has a square hole in its end to receive the end of a short arbor, e, (fig. 4.) which is an enlarged plan of the wheel-work; this end has an endless screw on it, turning a wheel, f; below this wheel, on the same arbor, is a pinion turning a wheel, h, and lower still is another wheel (hidden by ƒ), turning a pinion, g, on whose arbor is the small hand, i, shewn in the plan of the dial plate. The wheel, h, has a pinion on its arbor, immediately above it, turning k, which has a pinion above it, turning 1, whose arbor is a tube, and put over the orb of h; this tube has a short hand, m, (fig. 5.) fixed on it. The long hand, n, is fixed to the arbor of the wheel h; this ar bor is not made fast to the wheel, but to a circular plate, p, against which the wheel fits, and to which it is held by a pin put through the arbour beneath it, by this means the hands can be turned round to set them, without moving the wheel h; a pin is fixed in this wheel, which a, every revolution, lifts and lets falls a hammer, r, to strike the bell, t, and thus give notice of the hand having completed its revolution. The great wheel is half a pole in circumference, and the wheels a b, being equal, the endless screw turns once for every half pole the instrument is wheeled along the ground; the screw is so cut, that it turns the wheel, f, once in twenty.

=

= 1

four turns of the great wheel, equal twelve poles. The lower wheel on its arbor has thirty-six teeth, and turns g, of twelve teeth, three times as fast, or once for four poles; this is equal to one chain, and the circle of the hand, i, (fig. 5.) which it carries, is divided into one hundred, each equal one link; the pinion on the arbor of has twelve teeth, and h, which it turns, has forty, it will turn once for 34 times of f, or 31 times 12 poles 40 poles furlong; the dial of the hand, n, which it carries, is divided into forty, each equal one pole, and by the pin in the plate, p, it strikes the bell once each revolution. The pinion of eight on the arbor of h, turns k of sixty-four once for eight furlongs, and its pinion of six drives of seventy-two once round for twelve of k, or ninety-six furlongs, equal twelve miles. The hand, m, fixed to its arbor, points out these distances on a circle divided into twelve for miles, and subdivided into eight for furlongs. A small scraper is fixed to the frame to prevent the wheel gathering dirt, and thus enlarging its circumference.

In wheeling a machine along a road, care should be taken to avoid all sudden holes or hills, as much as possible, without deviating from the straight line.

The bell, by striking, is of great use to point out every furlong, which might otherwise be passed unnoticed.

PERCA, the perch, in natural history, a genus of fishes of the order Thoracici. Generic character: jaws unequal; teeth sharp and incurvated; gill-covers of three lamina, scaly and serrated; dorsal fin spiny on the fore part; scales generally hard and rough. There are sixty species, of which the following is most deserving

of notice.

P. fluviatilis, or the common perch of England, is generally from one to two feet long, and two pounds and a half in weight, and inhabits the clear fresh waters of almost every country in Europe, sometimes attaining the weight of ten pounds. It is gregarious, haunts those parts where the stream is gentle and profound, is extremely rapacious, catches with avidity at almost any bait, and tenacious of vitality to an extraordinary degree, surviving a journey of fifty miles, though packed up in dry straw. It is highly valued both for its firmness and flavour, and among the Romans was held in very superior estimation.

P. striatus. Pale brown or whitish, with about eight lines running parallel with each other on the sides. This is the fish