known by the name of "Rock fish," and in some districts by that of "Basse." It is brought to our markets in great numbers during the winter, and is in high estimation as food. Doctor Mitchill is per. haps the first describer of the,, Rock," under the specific name which we have here adopted; he has subsequently thought proper to reject this appellation, and has substituted his own name, Mitchili. But as he gives us no reason whatever for an alteration of so much importance, we cannot concur in adopting it. We do not know of any fish belonging to the genus, as it now stands, to which the same name has been applied: the P. striatus of Linn. is not a true Perca according to the late arrangements, and therefore cannot be taken into consideration in this case by any one who adopts these arrange ments. PERCEPTION, in logic, the first and most simple act of the mind, whereby it perceives or is conscious of its ideas. In bare perception, the mind is for the most part only passive; yet impressions made on the senses cause no perception, unless they are taken notice of by the mind, as we see in those who are intently busied in the contemplation of certain objects. It ought also to be observed, that the ideas we receive by perception are often altered by the judgment, without our taking notice of it; so that we take that for the perception of our senses, which is but an idea formed by the judgment: thus a man who reads or hears, with attention, takes little notice of the characters or sounds, but of the ideas excited in him by them. The faculty of perception seems to be that which constitutes the distinction between the animal kingdom and the inferior parts of nature. Perception is also the first step towards knowledge, and the inlet of all the materials of it; so that the fewer senses a man has, and the duller the impressions that are made by them are, the more remote he is from that knowledge which is to be found in other men. PERCH, or PEARCH. See PERCA. PERCH, a measure of length equal to five yards and a half. See MEASURE. PERCUSSION, in mechanics, the impression a body makes in falling or striking upon another, or the shock of two bodies in motion. See MOTION. Percussion is either direct or oblique; direct, when the impulse is given in a line perpendicular to the point of contact; and oblique, when it is given in a line oblique to the point of contact. The ratio which an oblique stroke bears to a perpendicu lar one, is as the sine of the angle of incidence to the radius. Thus, let a b (Plate XII. Miscel. fig. 13.) be the side of any body on which an oblique force falls, with the direction da; draw d c at right angles to db, a perpendicular let fall from d to the body to be moved, and make a d the radius of a circle: it is plain that the oblique force da, by the laws of composition and resolution of motions, will be resolved into the two forces dc and b d; of which d c, being parallel to a b, hath no energy or force to move that body; and, consequently, db expresses all the power of the stroke or impulse on the body to be moved: but db is the right sine of the angle of incidence, d a b; wherefore the oblique force da, to one falling perpendicularly, is as the sine of the angle of incidence to the radius. PERDICIUM, in botany, a genus of the Syngenesia Polygamia Superflua class and order. Natural order of Compositæ Discoidea. Corymbiferæ, Jussieu. Essential character: corollets bilabiate; down simple; receptacle naked. There are six species. PERENNIAL, in botany, is applied to those plants whose roots will abide many years, whether they retain their leaves in winter or not: those which retain their leaves are called ever-greens; but such as cast their leaves are called deciduous. Some of these have annual stalks, which die to the root every autumn, and shoot up again in the spring. PERFECT, in arithmetic. Perfect number is that, all whose aliquot parts, added together, make the same number with the number whereof they are such pafts. Thus six is a perfect number, being equal 1+ 2+3: so also is 28=1+2+4+7+14. Mathematicians have been at considerable pains to investigate the perfect numbers, but with no great success, the following are given as the first six perfect numbers: 6 28 496 8128 33550336 8589869056 PERGULARIA, in botany, a genus of the Pentandria Digynia class and order. Natural order of Contorta. Apocineæ, Jussieu. Essential character: contorted nectary, surrounding the gentials with five sagittated cusps; corolla salver-shaped. There are five species. PERIANTHIUM, in botany, the flower cup, properly so called, the most common species of calyx, placed immediately under the flower, which is contained in it as a cup. The flower cup differs in point, number, figure, proportion, and situation. PERICARPIUM. See BOTANY. PERICRANIUM, in anatomy, a thick solid coat, or membrane, covering the outside of the cranium or skull. PERIGEE, in astronomy, that point of the sun's or moon's orbit, wherein they are at their least distance from the earth, in which sense it stands opposed to apogee. PERIHELIUM, in astronomy, that point of a planet's or comet's orbit, wherein it is in its least distance from the sun; in which sense it stands in opposition to aphelium. PERILLA, in botany, a genus of the Didynamia Gymnospermia class and order. Natural order of Verticellatæ. Labiatæ, Jussieu. Essential character: calyx, uppermost segment very short; stamens distant; styles two, connected. There is but one species, viz P. ocymoides, an annual plant, and a native of the East Indies. PERIMETER, in geometry, the bounds or limits of any figure or body. The perimeter of surfaces or figures are lines, those of bodies are surfaces. In circular figures, instead of perimeter, we say circumference, or periphery. PERINEUM, or PERINEUM. See ANATOMY. PERIOD, in astronomy, the time taken up by a star or planet in making a revolution round the sun; or the duration of its course till it return to the same point of its orbit. See ASTRONOMY. There is a wonderful harmony between the distances of the planets from the sun, and their periods round him: the great law whereof is, that the squares of the periodical times of the primary planets are to each other as the cubes of their distances from the sun; and likewise, the squares of the periodical times of the secondaries of any planet are to each other as the cubes of their distances from that primary. This harmony among the planets is one of the greatest confirmations of the Copernican hypothesis. PERIOD, in chronology, denotes a revolution of a certain number of years, or a series of years, whereby, in different nations, and on different occasions, time is measured; such are the following. PERIOD, Calippic, a system of seventysix years. The calippic period comprehends 48 common years, and 28 inter calary ones, 940 lunations, and 22,759 days. See CHRONOLOGY. PERIOD, Dionysian, or Victorian PERIOD, a system of 532 luna-solar and Julian years, which being elapsed, the characters of the moon fall again upon the same day and feria, and revolve in the same order, according to the opinion of the ancients. This period is otherwise called the great paschal cycle, because the Christian church first used it to find the true time of the pascha, or easter. The sum of these years arise by multiplying together the cycles of the sun and moon. See EASTER. PERIOD, Hipparchus's, a system of 304 years, both lunar and solar, which being elapsed, Hipparchus thought that the reckoning by the lunar motion would coincide again with the solar measures. This period comprehends 3760 lunar months, or 111,039 days; the sum of which arises from the multiplication of the calippic period by 4, subtracting unity from the product. PERIOD, in grammar, denotes a small compass of discourse, containing a perfect sentence, and distinguished at the end by a point or full stop, thus (.); and its members or divisions marked by commas, colons, &c. PERIOD is also used for the character (.) wherewith the periods of discourse are terminated, or expressed, being commonly called a full stop or point. See PUNCTUATION. PERIOD, in numbers, a distinction made by a point, or comma, after every sixth place or figure; and is used in numeration, for the readier distinguishing and naming the several figures or places, which see under ARITHMETIC. PERIOECI, in geography, such inhabitants of the earth as have the same latitudes, but opposite longitudes; or live under the same parallel and the same meridian, or in opposite semicircles of that meridian, or in opposite points of the parallel. These have the same common seasons throughout the year, and the same phenomena of the heavenly bodies; but when it is noon day with the one, it is midnight with the other, there being twelve hours between them in an east or west direction. These are found on the globe by the hour-index, or by turning the globe half round, that is, 180 degrees either way. PERIOSTEUM, or PERIOSTIUM, in anatomy, a nervous vasculous membrane, endued with a very quick sense, immediately surrounding in every part PER both the internal and external surfaces of all the bones in 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. PERIPATETIC philosophy, that system taught and established by Aristotle, and maintained by his followers, the Peripatetics, called also Aristotelians. The philosophy of Aristotle may be divided into three distinct branches; instrumental, theoretical, and practical. Under the first head are included his doctrines concerning logic; under the second, his principles of physics, pneumatology, ontology, and mathematics; and under the third, his system of ethics and policy. Upon all these we cannot enlarge; but shall refer to his doctrine concerning the human mind and animal life. Aristotle, having undertaken to teach a new system of philosophy, was desirous of receding as far as possible from former philosophers, and particularly from Plato; and in treating upon any subject on which he had no doctrine to offer, he gave old opinions the air of novelty, by clothing them in new language. This latter method he adopted on the subject of mind. He asserted, with Plato, that there are in men different faculties, which have respectively a different organ; but he designedly expressed his doctrine upon this head in obscure terms, which cannot be explained with entire perspi cuity without supposing, as many writers have done, what Aristotle ought to have taught, instead of endeavouring to discover what he actually did teach. His leading tenets on this subject are these: The soul is the first principle of action in an organized body, possessing life potentially. The soul does not move itself; for whatever moves is moved by some other moving power. It is not a body, composed of elements; for then it would not have perception more than the elements which compose it. The soul has three faculties, the nutritive, the sensitive, and the rational; the superior comprehending the inferior potentially. The nutritive faculty is that by which life is produced and preserved. The sensitive faculty is that by which we perceive and feel; it does not perceive itself nor its organs, but some external objects, through the intervention of its organs, which are adapted to produce the sensations of sight, hearing, smell, taste, and touch. The senses receive sensible species, or forms, without matter, as wax receives the impression of a seal, without VOL. IX. rare PER It is receiving any part of its substance. The external senses perceive objects; but it is the common, or internal sense, which observes their difference. The internal sense perceives various objects at the intellect, the former being common to all same instant. Perception differs from animals, the latter to a few. Fancy is the perception produced in any animal, by the immediate action of the senses. accompanied with different feelings, according to the nature of the object by which it is produced. Memory is derived from fancy, and has its seat in the of some image impressed upon the soul same power of the soul. It is the effect by means of the senses. image cannot be retained, through an Where this excess of moisture or dryness in the temperature of the brain, memory ceases. Reminiscence is that faculty of the mind, by which we search for any thing which we wish to recollect through a series of things nearly related to it, till at last we intellect is that part of the soul by which call to mind what we had forgotten. The it understands. It is of two kinds, passive and active. Passive intellect is that faculty by which the understanding receives the forms of things: it is the seat of species. Active intellect is the efficient cause of all knowledge; and is either simple, when it is employed in the near apprehension of its object; or complex, when it compounds simple conceptions, in order to produce belief and assent. The latter is either true or false, the former neither. The action of the intellect is either theoretical or practical; theoretical, when it simply considers what is true or false; and practical, when it judges whether any thing is good or evil, and hereby excites the will to pursue or avoid it. The principle of local motion is the desire, or aversion, which arises from the practical exercise of the understanding. This desire, or aversion, produces either rational volition or sensitive appetite. The production of animal life arises from the union of the nutritive soul with animal heat. Life is the continuance of this union; death, its dissolution. The nature of the first principle of animal life, and of all perception, intelligence, and action, Aristotle, as well as all other philosophers, was at a loss to explain. Having no other way of judging concerning it than by observing its operations as far as they are subjects of experience, he could only define the mind to be that principle, by which we live, perceive, and understand. When he at Y tempted to form an abstract conception of this principle, he saw that there must be some substance, which enjoys such perfection as to be capable of performing this function; but he was wholly ignorant of the nature of this substance, and therefore, in defining it, he made use of a term expressive of the confused idea which he had formed to himself from observing its operations, and called it perfect energy; that is, if he had confessed the truth, some substance which is adapted to produce sensitive and rational life in certain organized bodies. This term will afford the attentive reader a striking example of the manner in which Aristotle endeavoured to explain the principles of nature, by vague notions and unmeaning words. But on other subjects he is sometimes remarkably clear, as in his discussion on "Politics" he states in a few words, the only legitimate purpose of political establishments. 66 Every political society forms, it is plain, a sort of community or partnership, instituted for the benefit of the partners. Utility is the end and aim of every such institution: and the greatest and most extensive utility is the aim of that great association comprehending all the rest, and known by the name of the commonwealth." Having stated and explained the grand purposes of society, he considers the best systems of means for attaining those purposes, and traces the distinction of ranks which arises from the inequalities of individual talents, virtue, and fortune. Political institutions are best fitted for promoting human happiness, when they are most suitable to the opinions and sentiments of the people, and the circumstances of the times and country. No one political system will equally suit all situations, and scarcely any two. Government being an arrangement, the best government must be the best arrangement, and the best arrange. ment is that in which the materials to be arranged are the best fitted both to receive and to preserve. The materials of the statesman or legislator are the number and character of his people, and the extent and quality of his country. The excellence of a commonwearth, however, is not to be estimated by its populousness or extent, but by its fitness for performing its proper functions: the same energies and habits constitute the happiness both of individuals and of nations. Men make governments, not governments them: nor by any sys tem of political arrangements can a hap py commonwealth be constituted from fools or cowards, profligates or knaves. The bricks must be first prepared before the edifice can be reared. The human character is a compound of good and evil: the former arises from the balance of the affections, under the control and guidance of reason, the latter results from passion operating without restraint. That government is the best which most powerfully stimulates the energies of the people to beneficial purposes, and restrains them from hurtful pursuits. That must be a system of freedom, in the first place tempered by order, and moderation in the second. Mixed governments, wisely formed and balanced, best correspond to the state of mankind. Democra cy, though apparently most agreeable to the rights of man, is not the best adapted to his wants; the general will, unrestrained, is apt to run into excess; to be precipitate in deliberation, and tardy in execution. While simple democracy is inexpedient for the people themselves, simple aristocracy and simple monarchy are equally inexpedient; and being the subjection of the many to a few, or to one, are moreover unjust. For these reasons Aristotle recommends a constitution that combines and balances the three orders, as the most generally likely to promote the good of society. To his "Treatise on Politics" Aristotle has added two books on "Oeconomics," in which he has treated in a similar way on the management of domestic concerns. Nothing is to be met with in the writings of Aristotle, which decisively determines whether he thought the soul of man mortal or immortal; but the former appears most probable, from his notion of the nature and origin of the human soul, which he conceived to be an intellectual power, externally transmitted into the human body from an Eternal Intelligence, the common source of rationality to human beings. Aristotle does not inform his readers what he conceived this universal principle to be; but there is no proof that he supposed the union of this principle with any individual to continue after death. PERIPHERY, in geometry, the circumference of a circle, ellipsis, or any other regular curvilinear figure. PERIPLOCA, in botany, a genus of the Pentandria Digynia class and order. Natural order of Contorta. Apocineæ, Jussieu. Essential character: nectary encircling the gentials, and putting forth five threads. There are thirteen species, of which P. græca, common Virginian silk, or periploca, has shrubby twining stems, covered with a dark-coloured bark, sending out slender branches, twining round each other: leaves ovate, lanceolate, nearly four inches long, and two broad in the middle; of a lucid green on their upper side, paler underneath, opposite on short foot-stalks; the flowers appear near the ends of the small branches in bunches of a purple colour, in the months of July and August. PERIPTERAL, in architecture, surrounded on all sides with columns, equidistant from the walls of a building. PERISCH, in geography, the inhabitants of either frigid zone, between the polar circles and the poles; where the sun, when in the summer signs, moves only round about them, without setting, and consequently their shadows, in the same day, turn to all the points of the horizon. PERISTALTIC, in medicine, 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 are composed by means whereof the chyle is driven into the orifices of the lacteal veins, and the fæces are protruded towards the anus. : PERITROCHIUM, in mechanics, denotes a wheel, or circle, concentric with the base of a cylinder, and moveable together with it about an axis. See ME CHANICS. PERIWINKLE. See BUCCINUM. PERMIT, a license or warrant for persons to pass with or sell goods, having paid the duties of customs and excise. PERMUTATION of quantities, in algegra, the same with combination. See COMBINATION. PERORATION, in rhetoric, the epilogue, or last part of an oration, wherein what the orator had insisted on through his whole discourse is urged afresh with greater vehemence and passion. The peroration consists of two parts: 1. Recapitulation, wherein the substance of what was diffused throughout the whole speech is collected briefly and cursorily, and summed up with new force and weight. 2. The moving the passions, which is so peculiar to the peroration, that the masters of the art call this part sedes affectuum. The passions to be raised are various, according to the various kinds of oration. In a panegyric, love, admiration, emulation, joy, &c. In an invective, hatred, contempt, &c. In a deliberation, hope, confidence, or fear. The qualities required in the peroration are, that it be very vehement and passionate, and that it be short; because, as Cicero observes, tears soon dry up. PEROTIS, in botany, a genus of the Triandria Digynia class and order. Essential character: calyx none; corolla two-valved; valves equal, awned. There are two species, viz. P. latifolia, and P. polystachya, both natives of the East Indies. PERPENDICULAR, in geometry, a line, falling directly on another line, so as to make equal angles on each side; called also a normal line. See GEOMETRY. PERPENDICULAR to a parabola, is a right line cutting the parabola in the point in which any other right line touches it, and is also itself perpendicular to that tangent. PERPETUAL Screw, is one which is acted upon by the teeth of a wheel, and which continues its action for an indefinite length of time, or as long as the teeth of the wheel continue to act upon it. PERPETUITY, in the doctrine of an-, nuities, 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 forever; and it is found by dividing 1002. by the rate of interest agreed upon thus allowing 5 per cent. the per100 petuity is £ = 20; and at the rates 5 usually adopted, the perpetuity is as follows: |