placed according to the taste, that is the arbitrary choice of the writer; and particularly in such a manner as shall render the enunciation agreeable to his ear. This view of the subject, however, is so far from being just, that, in reality, the points have nothing to do with the ear. The sense of which the ear is the organ, is to be satisfied by the harmony of the style, not by mere punctuation.

PERIOECI, in geography, such inhabitants of the earth, as have the same latitudes, but who live in opposite longitudes; or live under the same parallel, and the same meridian, but in different semicircles of that meridian. These have the same common seasons throughout the year, but when it is noon-day with one, it is midnight with the other.

PERIOSTEUM, in anatomy, a nervous, vasculous membrane, éndued with a very quick sense, immediately surrounding, in every part, both the internal and external surfaces of all the bones of the body, excepting only so much of the teeth as stand above the gums, and the peculiar places on the bones in which the muscles are inserted it is hence divided into the external and internal periosteum ; and where it externally surrounds the bones of the skull, it is usually called the pericranium: The seeming sensibility of the bones is that of this membrane.

PERIPATETIC philosophy. See PHILOSOPHY, peripatetic.

PERISCII, in geography, the inhabitants of either frigid zone between the polar circles and the poles, where the sun, when in the summer signs, appears to move only round them, without setting, and consequently their shadows, in the same day, turn to all the points of the horizon.

PERISTALTIC motion, a vermicular spontaneous motion of the intestines performed by the contraction of the circular and longitudinal fibres of which the fleshy coats of the intestines is composed, by means of which the chyle is driven into the orifices of the lacteal veins, and the fœces driven forwards.

PERJURY, in law, the crime of swearing falsely, where a lawful oath is administered by one in authority, in a matter relating to the issue or cause in question, whether it be a person's own wilful act, or one committed at the subornation of another.

PERORATION, in rhetoric, the epilogue, or last part of an oration, wherein what the orator insisted on through his whole discourse is urged afresh with greater vehemence. The peroration consists of two parts: a rapid recapitulation of what has been said before; and a declamatory address to the pas. sions. The qualities requisite in the peroration are, animation and brevity.

t

PERPENDICULAR, in geometry, a line falling directly on another line, so as to make the angles on each side equal.

PERPETUAL Screw, is one that is acted upon by the teeth of a wheel, and which continues its action for an indefinite length of time, or so long as the teeth of the wheel continue to act upon it.

PERPETUITY, is the number of years in which the simple interest of any principal sum will amount to the same as the principal itself: or it is the number of years purchase to be given for an annuity which is to continue for ever; and it is found by dividing 100l. by the rate of interest

agreed on : thus allowing 5 per cent. the perpetuity

20: if 4 or 6 per cent. be the interest

agreed on, then the perpetuity in one case will be

100

= 25, in the other

100

6

16.66.

PERSIA, a country in Asia, is bounded on the North by Russia, the Caspian sea, and Independent Tartary, on the East by the Mogul empire, from which a ridge of mountains, and the river Indus divide it: on the South it has the Arabian Sea, and the Persian gulf, and on the West it has Georgia, Curdistan, Armenia, and Arabia. It is about 1150 miles in length North and South, and 1280 from West to East. These are the greatest measures, and in some parts it is much narrower.

The tem

perature and climate are various; at about a league's distance from Ispahan, there is a stone four feet high, and when the snow happens to cover the ground to that height, it is the sign of a plentiful year. The first peasant who carries the news of it to the court receives a handsome reward, equal to 2301. sterling. It rarely rains in this country, excepting in the month of April, and the heat, in some parts, is so great as to induce mortal diseases upon the weak and the intemperate. The lands are exceedingly fertile, corn quickly ripens, and, in particular districts, they have three crops in a year. The fruits are excellent: the celebrated Shiraz wine is the produce of their grapes. The government is monarchical, and the religion that of Mohammed. The laws of Persia exclude the blind from the throne, hence the reigning prince usually

orders the eyes of all the males of the royal family, of whom he entertains any jealousy, to be put out.

PERSONIFICATION, the attributing of life and action, to an object or idea by the act of the imagination.

PERSPECTIVE, that branch of optics which teaches how to represent objects on a plane surface, in the manner they appear under the peculiarities incident to distance and height. This is a science of the first importance to the painter; yet he is not to be too strictly confined to its rules, but to make them subservient to his own purposes. Nothing should tie up his hands: he should not have his genius imprisoned; but be at liberty to express his idea, with one stroke of his pencil; and, as Fresnoy counsels, "let the compasses be rather in his eyes than in his hands:" there let him measure distinctly every object by comparison, the principal talent that he should own. If he is well acquainted with the principles of his art, he will not stop at the dry rules of geometry, while his fancy is sketching all the principal parts of the picture; but proceed with the whole, and when the design is fixed, correct such parts as require it by the laws of perspective.

Perspective in a practical sense is the art of drawing, according to the principles of geometry, the true representations of real objects. Suppose we view a point situated beyond an upright transparent plane, as a glass window, the spot where a straight line from the eye to this point will go through the window is the perspective representation of it for the eye views all objects by means of rays of light, which proceed from it, to the dif

férent points of the object, in straight lines, thus Plate Perspective, fig. 1. shews the whole art of perspective: let E be the eye, NE its height from the ground O P, and R S T V a square object laid flat upon the ground. Now it is evident, that the eye will see the object R S T V, by means of the rays of light which come from every part of the object to the eye. Let us therefore suppose a transparent plane, A K, like a glass-window, to be fixed perpendicularly upon the ground O P, between the spectator N E and the object RS TV; and it will be evident, that the rays RE, SE, TE, and V E, will be cut by the transparent plane A K in the points r, s, t, v; which points are called the projections, or in other words, the perspective representations of the corresponding points R, S, T, V, of the original object. And if lines are drawn from the several points r, s, t, v, so as to join each other, the figure so described will be the projection or perspective representation of the whole original figure R STV upon the picture.

In like manner, suppose R S T V, fig. 2, to be raised perpendicular to the ground O P, and parallel to the picture, but every tlling else remaining in the same situation as in the former figure; then will r s to be the representation of R S T V: for it is the section of the picture with the rays RE, SE, TE and V E, which come from the original object to the eye. And here let us observe, that when the original object is parallel to the picture, its representation, r s t v, will not only be parallel to the original, but exactly like it, though smaller in proportion as the original object is farther from the picture; and if the original be