ish tinge, in the horizon, whilst their color and that of the air become one. The proportion of this degradation, as it is called, is regulated by the purity of the air, being greater according as there is more vapor in the air. Hence distant objects in a clear southern air appear much nearer than they really are, to an eye accustomed to a thick northern atmosphere. As the air changes, the aerial perspective must change. Morning, noon, evening, moonshine, winter, summer, the sea, &c., all have their different aerial perspective. In aerial perspective, the weakening of the tints corresponds to the foreshortening of the receding lines in linear perspective. In the illuminated parts of objects, the tints are represented more broken and fluctuating. The shaded parts are often aided by reflection. If the degree of the density of the air is given, the degrees of these gradations may also be determined; not by mathematical rules, indeed, but by close observation of nature. By aerial perspective two results are obtained:-1. each object in a picture receives that degree of color and light which belongs to its distance from the eye; 2. the various local tones are made to unite in one chief tone, which is nothing else than the common color of the air, and the light which penetrates it. The charm and harmony of a picture, particularly of a landscape, depend greatly upon a correct application of aerial perspective. Aerial perspective is hardly found at all in the productions of the ancient German and Italian schools to the time of Perugino. (q. v.)-Valencienne's Practical Introduction to Linear and Aerial Perspective (in French) is very good. Beginners in linear perspective will find Easy Lessons in Perspective (Boston, 1830) a convenient manual.

PERSPIRATION. By perspiration from the bodies of beasts and men, we understand, 1. that operation by which certain fluid matters, separated from the blood in the thick network of capillary vessels and cells constituting the skin, are changed into vapor (or into fine effluvia), and in this form escape at the pores of the skin; 2. sometimes, also, the secretion and removal from the body of these matters themselves, by the action of the skin. This effluvium is usually so fine, that we cannot see it with the naked eye, whence we call it the "insensible perspiration"; but it becomes visible, if we hold the hand on cold glass or polished metal; also, if the perspiration is strong, in a cold temperature, or if, from a still stronger perspiration, this vapor is not dissolved in the

air, but collects on the skin in drops forming sweat. This perspiration through the skin has much resemblance to the vapor that escapes from the lungs, to the secretions of the membranes lining the cavities of the body, as the stomach, chest, and abdomen, with which secretions it also appears to stand in connexion. The importance of this function will be evident when we reflect, that the surface of a full grown man contains fifteen or sixteen square feet, and therefore the quantity of matter incessantly perspired must be very great, which is also confirmed by the accurate observations of Sanctorius (Venice, 1611), who spent a great part of his life at the balance. He weighed and kept an account not only of all the food that he consumed, but also of every thing that passed from him, and thereby proved that a great part not only of the fluid, but also of the solid substances that a man consumes, leaves his body by perspiration. Perspiration promotes two objects very important for the preservation of the bodily structure. One is the purification of the blood from injurious and superfluous matters. Besides the adventitious compound matters that pass into the blood from particular kinds of food (for instance, onions, &c.), the carbon, the hydrogen, and particularly the excess of nitrogen, are carried off from the blood by perspiration, and changed by caloric into gas and vapor, and thus removed from the body. The substance of the body is, in many diseases, particularly in fevers, converted into aeriform fluids by an evaporation so extraordinarily increased and accelerated, that the strongest man is entirely worn away in a few days, without having lost any thing except through his skin. The other advantage of perspiration is the preservation of a suitable degree of warmth in the body, and the reduction of an immoderate heat. Every living body has its peculiar degree of warmth, which remains for the most part the same, whether the surrounding bodies are more or less warm. The temperature of man is about 92° to 99° Fahrenheit. As much caloric is employed in the process of perspiration (see Evaporation), it is an important means of cooling the body and of conducting off the heat which is incessantly generated within. The greater the heat which the body is exposed to, or the more it is produced within from other causes, as hot drinks and excitement, the greater is the perspiration, and the more actively is the heat conducted off. If the body is exposed to great cold, the operations of the skin are

weakened, perspiration proceeds more slowly, caloric is more sparingly consumed, and thus accumulates in the body. Men usually lose flesh in summer, and recover it in winter, because the increased perspiration dissolves and removes more substance from the body in the former season. Therefore a man is cooled by sweat, and in the dry heat of a fever is refreshed as soon as a crisis produces perspiration. An interruption or even a disturbance of perspiration, for a long time, must then produce results in the highest degree prejudicial to the health, and even dangerous to life. These results in a great measure depend on the close connexion of the operations of the skin with those of the internal organs, and are the more stubborn and injurious the longer the perspiration is impeded. The increase of the internal warmth often produces a fever; also noxious matters are collected in the blood, from which it should be freed; therefore it changes from its natural condition, and an unnatural excitement is produced. Finally, the operation of the other organs of secretion is immoderately increased, because they have to perform in part the office of the skin: thence result, after a cold, rheum, sore throat, cough, also serious internal inflammations, diarrhæa, diabetes, dropsy, protracted rheumatism, and various other diseases. In a physiological view, William Cruikshank's Experiments on the Insensible Perspiration of the Human Body (London, 1795) deserves mention.

PERTH; a city of Scotland, capital of Perthshire, on the Tay, 39 miles north of Edinburgh; lon. 3° 27′ W.; lat. 56° 22′ N.; population, 20,000. It is situated on a low plain, under the Grampian hills: the scenery around it is very picturesque, and the approach to it is uncommonly beautiful. It has two beautiful meadows called Inches, each of which is about one and a half mile in circuit. It is a town of great antiquity, and has been the scene of many important transactions recorded in Scottish history. It contains various houses of public worship, a theatre, a celebrated grammar school, an academy, and a literary and antiquarian society, with a library. The staple manufacture is linen; but of late the cotton manufacture has almost superseded it. Besides these, there are extensive manufactures of leather, boots, shoes and gloves. The salmon fishery on the Tay, near Perth, is very extensive.

PERTURBATIONS of the course of planets are their deviations from their regular elliptic course, produced by their mutual

gravitation. The Newtonian discovery of the law of universal gravity threw much light on this important subject. Newton has shown that all bodies are attracted towards each other: hence every planet gravitates not only towards the sun, but also towards the other planets, the moon not only towards the earth, but particularly towards the sun; nay, even towards Venus and Jupiter. The regular course of the planets in elliptic orbits, according to Kepler's laws, is effected by the attraction of the sun, the course of the moon by the attraction of the earth; deviations must, therefore, naturally occur, in the motion of the moon and planets, if they are acted on also by other bodies. Newton explained and determined part of these deviations; for instance, the precession of the equinoxes and the nutation of the earth's axis. (See these articles.) But many problems which require the infinitesimal calculus for their solution, he left undetermined. Clairaut, D'Alembert and Euler subsequently occupied themselves with this subject; but even their solutions are only approximations. Laplace finally found a formula universally applicable, which gives the most exact results, and published the same in his Mécanique Céleste. This great work is so much condensed, that it requires a perfect knowledge of analysis, and is, therefore, unintelligible to many mathematical readers. Doctor Bowditch's translation and commentary, unfolding the processes by which the results are obtained, render the study of this work comparatively easy. Bohnenberger, in his Astronomy (Tűbingen, 1811), treats this subject in a less difficult manner than Laplace.

PERU; a republic of South America, formerly a Spanish viceroyalty, lying between 3° 20 and 21° 30 S. lat., and between 67° and 86° W. lon.; bounded N. by Colombia (Quito) and Brazil, to the E. by Brazil and Bolivia, or Upper Peru; to the S. by Buenos Ayres, and W. by the Pacific' ocean; square miles, 426,000; population, 1,700,000. In respect of physical geogra phy, Peru may be divided into the low country on the coast (with a hot climate, characterized by the total absence of rain, the want of which is imperfectly supplied by dew and mists from the ocean), and the highlands, which are formed by elevated ridges (sierras), beginning about 65 miles from the coast, and rising gradually to the Andes, of which, in fact, they are the lower steps. This latter region contains lofty plains, from 8000 to 10,000 feet above the level of the sea, and numerous deep

valleys. (See Andes, and South America.) The low districts on the coasts, which are supplied with water, or which lie on the streams and rivers, are fruitful. Besides the streams which flow down the western declivities of the Andes into the Pacific ocean, the Marañon or Amazon (q. v.), and the Ucayale, a tributary of the Amazon, are the principal rivers. The great plain, called the Pampas del Sacramento (see Pampas), on the Ucayale, is remarkable for its fertility. Earthquakes and sand-spouts sometimes commit terrible ravages. In the high lands the climate is severe, but healthy. Among the animal and vegetable productions of Peru are lamas, vicuñas, guanacos, pearl muscles, purple-fish, cochineal, silk-worms, corn, wine, tobacco, sugar, coffee, cocoa, vanilla, cotton, Peruvian bark, Peruvian balsam, indigo, ginger, cinnamon, &c. Peru is particularly rich in gold and silver. Humboldt reckoned the value of the quantity of these metals, obtained yearly, at more than $6,000,000. (See Mines, and South America.) Platina, copper, tin, lead, quicksilver, precious stones, salt, alum, saltpetre, coal, sulphur, &c., are also found. The capital of Peru is Lima. The republic is divided into seven intendencies Arequipa, Cusco, Guamanga, Guanca Velica, Lima, Tarma and Truxillo,-which are subdivided into provinces. An extensive tract of country in the north-eastern part, and not included in these divisions, is inhabited by independent Indians. The population is composed of European Spaniards, creoles (q. v.), metis or mestizoes (q. v.), Indians, negroes and mulattoes. The creoles are, since the revolution, the most influential class. The Indians and mestizos form the most numerous body. By the constitution of 1828, slavery is totally abolished, and a slave brought into the country becomes free. The wealth of Peru has been entirely owing to its mines, the richness of which, with the sterility of the soil, has prevented much attention being paid to agriculture. The whale fishery on the coasts, and the commerce of the country, are almost entirely in the hands of the Anglo-Americans of the U. States, and of the English. Its long extent of coast, with numerous bays, harbors and road-steads, affords great facilities for commerce. The exports of Peru are copper, cocoa, Peruvian bark, wool (of sheep and the vicuña), and chinchilla furs; imports, silk goods, linen, woollen goods, wine, cottons, &c. Mining operations are impeded by the deficiency of quicksilver and wood; there

are 4 copper, 4 quicksilver, 12 lead, and 680 silver mines, and 70 gold mines and washings. The richest silver mines are those of Pasco and Lauricocha; they lie 13,000 feet above the level of the sea, and yield $2,000,000 annually. The mines of Chota, or Gualgayoc, in Truxillo, are richer than those of Potosi; they are 13,385 feet above the level of the sea, and yield about 44,000 pounds of silver annually. Those of Huantajaya, in Arica, in a dry desert, yield yearly 52,000 pounds. Two masses of native silver have been found here, weighing, one 225, the other 890 pounds. Gold is obtained in Tarma, from the mines of Pataz and Huilies, and in the washings on the banks of the Upper Marañon. According to the traditions of the Peruvians, the early civilization of their country was the work of Manco Capac (q. v.), who reclaimed their ancestors from barbarism, and introduced art, law and religion among them. According to Garcilaso de la Vega (q. v.), this event occurred towards the beginning of the twelfth century. The successors of Manco Capac continued to reign until the arrival of the Spaniards in the country. Atahuallpa, the fifteenth inca (q. v.), was defeated and put to death by Pizarro (q. v.), who, with Almagro (q. v.), had entered Peru at the head of a small Spanish force, in 1532, and rapidly reduced it to submission. Of the ancient Peruvians, we have yet some remarkable monuments remaining, such as their roads (called by the Spaniards Camini del Inca), which traversed the empire in every direction, fortresses, temples and palaces, which prove their mechanical skill. They were acquainted with the arts of mining, of working in gold and silver, of polishing precious stones, and of sculpture. Their agricultural labors, and their manufactures of wool, &c., prove their intelligence and industry. (See Garcilaso de la Vega's Historia de las Antiguedades y Conquista del Peru.) Pizarro, having put the inca to death, took possession of Cusco and its immense treasures. The cruelties which were practised by the Spaniards, finally came to the ears of Charles V, who caused a code of laws to be drawn up for the government of the American conquests, and established an audiencia at Lima, the president of which was appointed governor of Peru, in 1543. Still the natives were subject to enormities of the most atrocious character, as long as the first murdering and robbing conquerors survived; and, for a long series of generations afterwards, to the most arbitrary and op

pressive acts of a cruel government. The timid and unwarlike Peruvians were repeatedly driven to rebel against their hard masters; one of the most celebrated of these revolts was that headed by Tupac Amaru, in 1780. (See Tupac Amaru.) In 1718, the province of Quito, which had previously formed a part of the viceroyalty of Peru, was annexed to New Grenada; and, in 1778, the provinces of Upper Peru (see Bolivia) were attached to the government of Buenos Ayres. On the invasion of the Spanish peninsula by the French, in 1808, the first symptoms of revolt began to show themselves in Peru, as in the other Spanish-American colonies; but the Spaniards were powerful enough to repress this spirit until 1821, when general San Martin, at the head of a Chilean force (see Chile), obtained possession of Lima, and the independence of Peru was declared (July 15). August 3d, general San Martin was declared protector of the new republic, with the supreme power, civil and military. Callao capitulated September 19. The Spanish generals La Serna and Canterac retreated to the mountains, and kept possession of Cusco. In March, 1822, the protector assembled a Peruvian congress at Lima, composed principally of his partisans, which drew up the plan of a constitution: it provided that the Catholic religion should be the religion of the state; that the legislative authority should be vested in the representatives of the people; that the freedom of the press, and the liberty of person and property, should be secured; the abolition of the slave-trade, of the tribute exacted from the Indians, and of the compulsory labor to which they had been subject, was provided for; a senate was to nominate to the executive authorities the civil and ecclesiastical officers, and, in extraordinary cases, convoke a congress. Much dissatisfaction was produced by this plan, as being too monarchical in its principles. In 1823, San Martin retired, and Lamar (q. v.) was placed at the head of the government, the marquis of Torretagle being governor of the capital. Meanwhile La Serna had maintained himself, and collected new forces in Upper Peru, and defeated the republican troops at Moquegna, Jan. 20, 1823. But the divisions of the Spanish commanders, La Serna, Valdez, Canterac and Olaneta, saved Peru. Riva-Aguero, who had assumed the presidency, called on the Colombians for assistance. General Sucre was despatched to the aid of the Peruvians; he compelled Canterac to evacuate Lima, which had

fallen into his hands, and advanced to Upper Peru, while Bolivar entered Lima, and received the title of libertador, with supreme military power. Bolivar obliged RivaAguero (who had still continued to exercise his authority in Truxillo) to surrender and leave the country, and, in November, the Peruvian congress adopted a constitution on the model of that of the U. States of North America, which was not to have effect until the expiration of Bolivar's dictatorship. La Serna had, meanwhile, collected a large army in Upper Peru, but was prevented from attempting any thing against the patriots, by the opposition of Olaneta, who was at the head of the absolutists, while La Serna had declared himself a constitutionalist. Torretagle, who had been declared president of the republic, was at the head of a party, which was working in secret against the influence of the liberator. Whilst things were in this state, the garrison of Callao (Feb. 5, 1824) hoisted Spanish colors, and opened the fortress to the Spanish ships of war which were blockading the harbor. In this emergency, congress conferred unlimited civil and military power on the dictator, who evacuated Lima on the 27th. Canterac entered the capital on the 29th, and Torretagle now joined the royalists. The war between the royalists was again renewed, and was again the means of saving Peru, Bolivar, having artfully drawn Canterac into the plains of Junin, gained some advantages over him on the 6th of August, and compelled the royalists to evacuate Lima; general Rodil, however, threw himself into Callao. After the patriots had suffered several disasters, Sucre fell back into an advantageous position, at Ayacucho, and determined to await the enemy. Dec. 9, 1824, the patriots, 5780 strong, were attacked by a royalist force of 9310, and gained a complete victory. La Serna and Valdez were made prisoners, and Canterac signed a capitulation on the field, by which it was stipulated that the royalist forces should lay down their arms, and evacuate the whole of the country, to the Desaguadero. The battle of Ayacucho (q. v.) was decisive of the fate of South America. General Rodil refused to surrender Callao, and that fortress held out till Jan. 22, 1826, when it was reduced by famine. Olaneta still maintained himself, for a time, in Upper Peru, but, in 1825, was totally routed by general Sucre. Of the events which followed in Peru, the suspicious conduct of Bolivar, and the constitution which he attempted to force upon the country, we have given an ac