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REFERENCES.-The literature dealing with the Permian and Permo-Carboniferous is very extensive; H. B. Geinitz, J. Marcou, Sir R. I. Murchison, Sir A. C. Ramsay, H. Potonié, R. Zeiller, O. Feist mantel, E. A. Newell, Arber, A. C. Seward, F. Bischoff, C. Ochsensius, E. Mojsisovics, V. Amalitzky, F. Noetling, C. Diener, A. Tschneryschew, A. Karpinsky, W. Waagen, H. F. and W. T. Blanford, G. H. Girty and very many others have made important contributions to the subject. Numerous references will be found in Sir A. Geikie, Textbook of Geology, 4th ed., and in the annual Geological Literature of the Geological Society of London. See also an interesting summary by C. Schuchert, "The Russian Carboniferous and Permian compared with those of India and America," Amer. Journ. Sci. (1906), 4th series, vol. xxii. pp. 29 seq. and a general account of the system in Lethaea geognostica, Th. I. Bd. II., F. Frech and others (Stuttgart 1897-1902). H. Everding, "Zur Geologie der deutschen Zechsteinsalze," Kgl. geolog. Landesanst. (Berlin, 1907) gives a full account of the salt and potassium-bearing beds. (J. A. H.)

PERNAMBUCO, a north-eastern state of Brazil, bounded N. by Ceará and Parahyba, E. by the Atlantic, S. by Alagoas and Bahia, and W. by Piauhy. Area, 49,573 sq. m.; pop. (1900), 1,178,150. It comprises a comparatively narrow coastal zone, a high inland plateau, and an intermediate zone formed by the terraces and slopes between the two. Its surface is much broken by the remains of the ancient plateau which has been worn down by erosion, leaving escarpments and ranges of flat-topped mountains, called chapadas, capped in places by horizontal layers of sandstone. Ranges of these chapadas form the boundary lines with three states-the Serras dos Irmãos and Vermelha with Piauhy, the Serra do Araripe with Ceará, and the Serra dos Cariris Velhos with Parahyba. The coastal zone is low, well-wooded and fertile. It has a hot, humid climate, relieved to some extent by the south-east trade winds. This region is locally known as the mattas (forests). The middle zone, called the caatinga or agreste region, has a drier climate and lighter vegetation. The inland region, called the sertão, is high, stony, and dry, and frequently devastated by prolonged droughts (sêccas). The climate is characterized by hot days and cool nights, and is considered healthy, though the daily change tends to provoke bronchial, catarrhal and inflammatory diseases. There are two clearly defined seasons, a rainy season from March | to June, and a dry season for the remaining months. The rivers of the state include a number of small plateau streams flowing southward to the São Francisco River, and several large streams in the eastern part flowing eastward to the Atlantic. The former are the Moxotó, Ema, Pajehú, Terra Nova, Brigida, Bôa Vista and Pontal, and are dry channels the greater part of the year. The largest of the coastal rivers are the Goyanna, which is formed by the confluence of the Tracunhaem and Capibaribe-mirim, and drains a rich agricultural region in the north-east part of the state; the Capibaribe, which has its source in the Serra de Jacarará and flows eastward to the Atlantic at Recife with a course of nearly 300 m.; the Ipojuca, which rises in the Serra de Aldeia Velha and reaches the coast south of Recife; the Serinhaen and the Una. A large tributary of the last-the Rio Jacuhipe, forms part of the boundary line with Alagoas.

Pernambuco is chiefly agricultural, the lowlands being devoted to sugar and fruit, with coffee in some of the more elevated localities, the agreste region to cotton, tobacco, Indian corn, beans and stock, and the sertão to grazing and in some localities to cotton. Sugar, molasses, rum (aguardente or cachaça), tobacco and fruit are largely exported. Coco-nuts, cacao, bananas, mangoes and other tropical fruits are produced in profusion, but the production of foodstuffs (beans, Indian corn, mandioca, &c.) is not sufficient for local consumption. Mangabeira rubber is collected to a limited extent, and piassava fibre is an article of export. Orchids are also collected for export in the districts of Garanhuns and Timbaúba. Cotton-weaving and cigar-making are the principal manufacturing industries, after the large engenhos devoted to the manufacture of sugar and rum. The railways of the state are the Recife and São Francisco (77 m.), Central de Pernambuco (132 m.) and Sul de Pernambuco (120 m.) --all government properties leased to the Great Western of Brazil Railway Co., Ltd., since 1901. Besides these there are the line from Recife to Limoeiro and Timbaúba (112 m.), with an

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extension from Timbaúba to Pilar (24 m.). All these lines concentrate at the port of Recife. The capital of the state is Recife, commonly known among foreigners as Pernambuco. There are a number of large towns in the state, but the census returns include their populations in those of the municipios (communes) to which they belong. The most important are: Bezerros (17,484), Bom Jardim (40,160), Brejo da Madre de Deus (13,655), a town of the higher agreste region, Cabo (13,337), Caruarú (17,844), Escada (9331), Garanhuns (32,788, covering six towns and villages), Gloria de Goytá (24,554), Goyanna, Limoeiro (21,576), Olinda (8080), the old colonial capital and episcopal see, Rio Formosa (6080), Timbaúba (9514) and Victoria (32,422).

Pernambuco was first settled in 1526 by Christovão Jacques who founded a settlement on the Rio Iguarassú that was afterwards abandoned. The first permanent settlement was made by Duarte Coelho Pereira at Olinda in 1530, and four years later he was granted a capitania of 50 leagues extending from the mouth of the São Francisco northward to that of the Iguarassú. Adjacent to this grant on the north was the capitania of Itamaracá, granted to Pero Lopes de Souza, which covered the remainder of the present state. The capitania of Pernambuco was ably governed and took an active part in the expulsion of the French from the trading posts established along the coast northward to Maranhão, and in establishing Portuguese colonies in their places. In 1630 Pernambuco was occupied by the Dutch and continued under their rule until 1654. Although an active guerrilla warfare was waged against the Dutch during a large part of that period, they did much to promote the agricultural and commercial interests of the colony, especially under the wise administration of Maurice of Nassau. In 1817 Pernambuco was the scene of a revolutionary outbreak, which resulted in the separation of the present states of Alagoas and Rio Grande do Norte, Ceará and Parahyba having been detached in 1799. There was another insurrection in 1822 when the Portuguese captain-general, Luiz de Rego, and his garrison was expelled, and in 1824 dissatisfaction with the arbitrary proceedings of Dom Pedro I. at Rio de Janeiro led to a separatist revolution for the formation of a new state, to be called the Federação do Equador. There was another outbreak in 1831 and frequent disorders down to 1848, when they culminated in another unsuccessful revolution. The population of the Pernambuco sertão has always been noted for its turbulent, lawless character, due partly to distance from the coast where the bulk of the population is concentrated, partly to difficult means of communication, and partly to the fact that this remote region has long been the refuge of criminals from the coast towns.

PERNAU (in Russ. Pernov and in Esthonian Pernolin), a seaport and watering-place of western Russia, in the government of Livonia, 155 m. N. of Riga, on the left bank of the Pernau or Pernova, which about half a mile farther down enters the Bay of Pernau, the northern arm of the Gulf of Riga. Pop., 12,850. The harbour is usually free from ice from the end of April to the middle of December.

Founded on the right side of the river in 1255 by one of the bishops of Oesel, Pernau soon became a flourishing place. In the 16th century it was occupied in succession by the Swedes, the Poles and the Teutonic Knights. After 1599 the Poles transferred the town to the left side of the river; and in 1642 the Swedes, who had been in possession since 1617, strengthened it with regular fortifications. In 1710 it was taken by the Russians, and the fortress is now demolished.

PERNE, ANDREW (c. 1519-1589), vice-chancellor of Cambridge University and dean of Ely, born about 1591, was son of John Perne of East Bilney, Norfolk. He was educated at St John's college, Cambridge, graduating B.A. in 1539, B.D. in 1547 and D.D. in 1552. He was elected fellow of Queens' in 1540, and vice-president in 1551, and was five times vicechancellor; but he owes his notoriety to his remarkable versatility, and, like the vicar of Bray, he was always faithful to the national religion, whatever it might be. In April 1547 he advocated Catholic doctrines, but recanted two months later, and his

Protestant faith was strengthened during Edward VI.'s reign; | at this locality large cubes occur with calcite and magnetite in he was appointed a royal chaplain and canon of Windsor. Soon a chlorite-schist. Similar crystals are also found in talc-schist after Mary's accession, however, he perceived the error of his at Zermatt in Switzerland. The microscopic octahedral ways and was made master of Peterhouse in 1554 and dean of crystals are characteristic of melilite basalt and nepheline Ely in 1557. He preached the sermon in 1556 when the bodies basalt; they have also been found in peridotite and serpenof Bucer and Fagius were disinterred and burnt for heresy, and tine. (L. J. S.) also in 1560 when these proceedings were reversed and the dead PEROWNE, JOHN JAMES STEWART (1823-1904), English heretics were rehabilitated. In Elizabeth's reign he subscribed bishop, was born, of Huguenot ancestry, at Burdwan, Bengal, the Thirty-nine Articles, denounced the pope and tried to on the 13th of March 1823. He was educated at Norwich and convert Abbot Feckenham to Protestantism; and in 1584 at Corpus Christi College, Cambridge, bcoming a fellow in 1849. Whitgift in vain recommended him for a bishopric. He died After holding a chair in King's College, London, he was appointed on the 26th of April 1589. He was selected as the type of vice-principal at St David's College, Lampeter (1862-1872). Anglican prelate by the authors of the Martin Mar-prelate In 1868 he was Hulsean lecturer, taking as his subject Immortracts and other Puritans, who nicknamed him "Old Andrew tality. He was elected canon of Llandaff in 1869, dean of PeterTurncoat," "Andrew Ambo," "Old Father Palinode." Cam- borough 1878, and in 1891 succeeded Henry Philpott as bishop bridge wits, it was said, translated "perno" by "I turn, I rat, of Worcester. Perowne was a good Hebrew scholar of the old I change often "; and a coat that had often been turned was type and sat on the Old Testament Revision Committee. He said to have been "perned." (A. F. P.) is best remembered as the general editor of the Cambridge Bible for Schools and Colleges. His chief works were a Commentary on the Book of Psalms (2 vols., 1864-1868) and a life of Bishop Thirlwall (1877-1878). He resigned his see in 1901, and died on the 6th of November 1904.

PÉRONNE, a town of northern France, capital of an arrondissement of the department of Somme, on the right bank of the Somme at its confluence with the Cologne, 35 m. E. by N. of Amiens by rail. Pop. (1906), 3698. The church of St Jean (1509-1525) was greatly damaged during the bombardment of 1870-71, but has since been restored. The castle of Péronne still retains four large conical-roofed towers dating from the middle ages, one of which is said to have been the prison of Louis XI. in 1468, when he was forced to agree to the "Treaty of Péronne." Péronne has a sub-prefecture, a tribunal of first instance and a communal college. Its trade and industry are of little importance.

The Frankish kings had a villa at Péronne, which Clovis II. gave to Erchinoaldus, mayor of the palace. The latter founded a monastery here, and raised in honour of St Fursy a collegiate church, which was a wealthy establishment until the Revolution; it is the burial-place of Charles the Simple, who died of starvation in a dungeon in Péronne, into which he had been thrown by the count of Vermandois (929). After the death of Philip of Alsace, Péronne, which he had inherited through his wife, escheated to the French Crown in the reign of Philip Augustus, from whom in 1209 it received a charter. By the treaty of Arras (1435) it was given to the Burgundians; bought back by Louis XI., it passed again into the hands of Charles the Bold in 1465. On the death of Charles, however, in 1477, Louis XI. resumed possession. In 1536 the emperor Charles V. besieged Péronne, but without success; in its defence a woman called Marie Fouré greatly distinguished herself. A statue of her stands in the town; and the anniversary of the raising of the siege is still celebrated annually. It was the first town after Paris at which the League was proclaimed in 1577. Péronne's greatest misfortunes occurred during the Franco-German War. It was invested on the 27th of December 1870, and bombarded from the 28th to the 9th of the following January, upon which date, on account of the sufferings of the civil population, among whom small-pox had broken out, it was compelled to capitulate.

PEROVSKITE, or PEROFSKITE, a mineral consisting of calcium titanate, CaTiO3, usually with a small proportion of the calcium replaced by iron. The crystals found in schistose rocks have the form of cubes, which are sometimes modified on the edges and corners by numerous small planes; on the other hand, the crystals occurring as an accessory constituent of eruptive rocks are octahedral in form and microscopic in size. Although geometrically cubic, the crystals are always doubly refracting, and they sometimes show evidence of complex mimetic twinning; their structure as shown in polarized light is very similar to that of the mineral boracite, and they are therefore described as pseudo-cubic. There are distinct cleavages parallel to the faces of the cube. The colour varies from pale yellow to blackishbrown and the lustre is adamantine to metallic; the crystals are transparent to opaque. The index of refraction is high, the hardness 5 and the specific gravity 4.0. The mineral was discovered at Achmatovsk near Zlatonst in the Urals by G. Rose in 1839, and named in honour of Count L. A. Perovsky;

PĒRŌZ (Peirozes, Priscus, fr. 33; Perozes, Procop. Pers. i. 3 and Agath. iv. 27; the modern form of the name is Feroz, Firuz, cf. FIRUZABAD), Sassanid king of Persia, A.D. 457-484, son of Yazdegerd II. He rebelled against his brother Homizd III., and in 459 defeated and killed him with the help of the Ephthalites, or White Huns, who had invaded Bactria. He also killed most of his other relatives, and persecuted the Christians. But he favoured the introduction of Nestorianism, in opposition to the orthodox creed of Byzantium. With the Romans he maintained peace, but he tried to keep down the Ephthalites, who began to conquer eastern Iran. The Romans supported him with subsidies; but all his wars were disastrous. Once he was himself taken prisoner and had to give his son Kavadh as hostage till after two years he was able to pay a heavy ransom. Then he broke the treaty again and advanced with a large army. But he lost his way in the eastern desert and perished with his whole army (484). The Ephthalites invaded and plundered Persia for two years, till at last a noble Persian from the old family of Karen, Zarmihr (or Sokhra), restored some degree of order. He raised Balash, a brother of Pērōz, to the throne. (ED. M.)

PERPENDICULAR PERIOD, the term given by Thomas Rickman to the third period of Gothic architecture in England, in consequence of the great predominance of perpendicular lines. In the later examples of the Decorated period the omission of the circles in the tracery had led to the employment of curves of double curvature which developed into flamboyant tracery, and the introduction of the perpendicular lines was a reaction in the contrary direction. The mullions of the windows (which are sometimes of immense size, so as to give greater space for the stained glass) are carried up into the arch mould of the windows, and the upper portion is subdivided by additional mullions. The buttresses and wall surface are likewise divided up into vertical panels. The doorways are frequently enclosed within a square head over the arch mouldings, the spandrils being fitted with quatrefoils or tracery. Inside the church the triforium disappears, or its place is filled with panelling, and greater importance is given to the clerestory windows which constitute the finest features in the churches of this period. The mouldings are flatter and less effective than those of the earlier periods, and one of the chief characteristics is the introduction of large elliptical hollows. The finest features of this period are the magnificent timber roofs, such as those of Westminster Hall (1395), Christ Church Hall, Oxford, and Crosby Hall.

The earliest examples of the Perpendicular period, dating from 1360, are found at Gloucester, where the masons of the cathedral would seem to have been far in advance of those in other towns. Among other buildings of note are the choir and tower of York Cathedral (1389-1407); the nave and western transepts of Canterbury Cathedral (1378-1411), and the tower

PERPENT, or PARPENT STONES, in architecture, bond or "through stones," the diaróvo of the Greeks and Romans, long stones going right through walls, and tying them together from face to face. The O. Fr. parpain, modern parpaing, from which this word is derived, is obscure in origin. It may be from a supposed Lat. perpago, perpaginis, formed like compago, a joint, from the root of pangere, to fasten, and meaning something fastened together," or from some popular corruption of Lat. perpendiculum, plummet or plumb-line (pir or pendere, to hang), referring to the smooth perpendicular faces of the stone.

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PERPETUAL MOTION, or Perpetuum MOBILE, in its usual significance, not simply a machine which will go on moving for ever, but a machine which, once set in motion, will go on doing useful work without drawing on any external source of energy, or a machine which in every complete cycle of its operation will give forth more energy than it has absorbed. Briefly, a perpetual motion usually means a machine which will create energy.

(towards the end of the 15th century); New College, Oxford | 19th century, yet so numerous are the cases in which it has been (1380-1386); the Beauchamp Chapel, Warwick (1381-1391); tested, so various the deductions from it that have been proved the nave and aisles of Winchester Cathedral (1399-1419); the to accord with experience, that it is now regarded as one of the transept and tower of Merton College, Oxford (1424-1450); | best-established laws of nature. Consequently, on any one who Manchester Cathedral (1422); the central tower of Gloucester calls it in question is thrown the burden of proving his case. If Cathedral (1454-1457), and that of Magdalen College, Oxford any machine were produced whose source of energy could not at (1475-1480). To those examples should be added the towers once be traced, a man of science (complete freedom of investiat Wrexham, Coventry, Evesham, and St Mary's at Taunton, gation being supposed) would in the first place try to trace its the first being of exceptional magnificence. power to some hidden source of a kind already known; or in the last resort he would seek for a source of energy of a new kind and give it a new name. Any assertion of creation of energy by means of a mere machine would have to be authenticated in many instances, and established by long investigation, before it could be received in modern science. The case is precisely as with the law of gravitation; if any apparent exception to this were observed in the case of some heavenly body, astronomers, instead of denying the law, would immediately seek to explain the occurrence by a wider application of it, say by including in their calculations the effect of some disturbing body hitherto neglected. If a man likes to indulge the notion that, after all, an exception to the law of the conservation of energy may be found, and, provided he submits his idea to the test of experiment at his own charges without annoying his neighbours, all that can be said is that he is engaged in an unpromising enterprise. The case is otherwise with the projector who comes forward with some machine which claims by the mere ingenuity of its contrivance to multiply the energy supplied to it from some of the ordinary sources of nature and sets to work to pester scientific men to examine his supposed discovery, or attempts therewith to induce the credulous to waste their money. This is by far the largest class of perpetual-motion-mongers nowadays. The interest of such cases is that attaching to the morbid anatomy of the human mind. Perhaps the most striking feature about them is the woful sameness of the symptoms of their madness. As a body perpetual-motion seekers are ambitious, lovers of the short path to wealth and fame, but wholly superficial. Their inventions are very rarely characterized even by mechanical ingenuity. Sometimes indeed the inventor has simply bewildered himself by the complexity of his device; but in most cases the machines of the perpetual motionist are of child-like simplicity, remarkable only for the extraordinary assertions of the inventor concerning them. Wealth of ideas there is none; simply assertions that such and such a machine solves the problem, although an identical contrivance has been shown to do no such thing by the brutal test of standing still in the hands of many previous inventors. Hosts of the seekers for the perpetual motion have attacked their insoluble problem with less than a schoolboy's share of the requisite knowledge; and their confidence as a rule is in proportion to their ignorance. Very often they get no further than a mere prospectus, on the strength of which they claim some imaginary reward, or offer their precious discovery for sale; sometimes they get the length of a model which wants only the last perfection (already in the inventor's brain) to solve the great problem; sometimes fraud is made to supply the motive power which their real or pretended efforts have failed to discover.

The earlier seekers after the "perpetuum mobile" did not always appreciate the exact nature of their quest; for we find among their ideals a clock that would periodically rewind itself, and thus go without human interference as long as its machinery would last. The energy created by such a machine would simply be the work done in overcoming the friction of its parts, so that its projectors might be held merely to have been ignorant of the laws of friction and of the dynamic theory of heat. Most of the perpetual motionists, however, had more practical views, and explicitly declared the object of their inventions to be the doing of useful work, such as raising water, grinding corn, and so on. Like the exact quadrature of the circle, the transmutation of metals and other famous problems of antiquity, the perpetual motion has now become a venerable paradox. Still, like these others, it retains a great historical interest. Just as some of the most interesting branches of modern pure mathematics sprang from the problem of squaring the circle, as the researches of the alchemists developed into the science of modern chemistry, so, as the result of the vain search after the perpetual motion, there grew up the greatest of all the generalizations of physical science, the principle of the conservation of energy.

There was a time when the problem of the perpetual motion was one worthy of the attention of a philosopher. Before that analysis of the action of ordinary machines which led to the laws of dynamics, and the discussion of the dynamical interdependence of natural phenomena which accompanied the establishment of the dynamical theory of heat, there was nothing plainly unreasonable in the idea that work might be done by the mere concatenation of machinery. It had not then been proved that energy is uncreatable and indestructible in the ordinary course of nature; even now that proof has only been given by induction from long observation of facts. There was a time when wise men believed that a spirit, whose maintenance would cost nothing, could by magic art be summoned from the deep to do his master's work; and it was just as reasonable to suppose that a structure of wood, brass and iron could be found to work under like conditions. The disproof is in both cases alike. No such spirit has ever existed, save in the imagination of his describer, and no such machine has ever been known to act, save in the fancy of its inventor.

The principle of the conservation of energy, which in one sense is simply denial of the possibility of a perpetual motion, rests on facts drawn from every branch of physical science; and, although its full establishment only dates from the middle of the

It was no doubt the barefaced fallacy of most of the plans for perpetual motion that led the majority of scientific men to conclude at a very early date that the "perpetuum mobile was an impossibility. We find the Paris Academy of Sciences refusing, as early as 1775, to receive schemes for the perpetual motion, which they class with solutions of the duplication of the cube, the trisection of an angle and the quadrature of the circle. Stevinus and Leibnitz seem to have regarded its impossibility as axiomatic; and Newton at the beginning of his Principia states, so far as ordinary mechanics are concerned, a principle which virtually amounts to the same thing.

The famous proof of P. De la Hire simply refers to some of the more common gravitational perpetual motions. The truth is, as we have said already, that, if proof is to be given, or considered necessary, it must proceed by induction from all physical phenomena.

1

It would serve no useful purpose here to give an exhaustive historical account of the vagaries of mankind in pursuit of the "perpetuum mobile." The reader may refer to Henry Dircks's Perpetuum Mobile (2 vols., 1861 and 1870), from which, for the most part, we select the following facts.

By far the most numerous class of perpetual motions is that which seeks to utilize the action of gravity upon rigid solids. We have not read of any actual proposal of the kind, but the most obvious thing to imagine in this way would be to procure some substance which intercepts gravitational attraction. If this could be had, then, by introducing a plate of it underneath a body while it was raised, we could elevate the body without doing work; then, removing the plate, we could allow the body to fall and do work; eccentrics or other imposing device being added to move the gravitation intercepter, behold a perpetual motion complete! The great difficulty is that no one has found the proper material for an intercepter.

Fig. I represents one of the most ancient and oftenest-repeated of gravitational perpetual motions. The idea is that the balls rolling in the compartments darwy between the felloe and the rim of the wheel will, on the whole, so comport themselves that the moment about the centre of those on the descending side exceeds the moment of those on the ascending side. Endless devices, such as curved spokes, levers with elbow-joints, eccentrics, &c., have been proposed for effecting this impossibility. The student of dynamics at once convinces himself that no machinery can effect any such result; because if we give the wheel a complete turn, so that each ball returns to its original position, the whole work done by the ball will, at the most, equal that done on it. We know that if the laws of motion be true, in each step the kinetic energy given to the whole system of wheel and balls is equal to that taken from the potential energy of the balls less what is dissipated in the form of heat by frictional forces, or vice versa, if the wheel and balls be losing kinetic energy-save that the friction in both cases leads to dissipation. So that, whatever the system may lose, it can, after it is left to itself, never gain energy during its motion.

TO O

FIG. 1.

The two most famous perpetual motions of history, viz. the wheels of the marquis of Worcester (d. 1667) and of Councillor Orffyraeus, were probably of this type. The marquis of Worcester gives the following account of his machine in his Century of Inventions (art. 56):

"To provide and make that all the Weights of the descending side of a Wheel shall be perpetually further from the Centre than those of the mounting side, and yet equal in number and heft to one side as the other. Å most incredible thing, if not seen but tried before the late king (of blessed memory) in the Tower, by my directions, two Extraordinary Embassadors accompanying His Majesty, and the Duke of Richmond, and Duke Hamilton, with most of the Court, attending him. The Wheel was 14. Foot over, and 40. Weights of 50. pounds apiece. Sir William Balfore, then Lieutenant of the Tower, can justify it, with several others. They all saw that no sooner these great Weights passed the Diameter-line of the lower side, but they hung a foot further from the Centre, nor no sooner passed the Diameter-line of the upper side but they hung a foot nearer. Be pleased to judge the consequence."

1 We here notice, so far as more recent times are concerned, may the claim of an American enthusiast, who, having worked a Hampson plant for liquefying air, stated that 3 lb of liquid air sufficed to liquefy ten, and of these tea seven could be employed as a source of motive power, whilst the remaining three could be utilized in the production of another 10 lb of the liquid gas. There was thus available an inexhaustible supply of energy! The absurdity of the proposition is obvious to any one acquainted with the laws of thermodynamics. Of more interest is the radium clock devised by the Hon. R. J. Strutt. This consists of a vacuum vessel from the top of which depends a short tube containing a fragment of a radioactive substance. At the lower end of this tube there are two gold leaves as in an electroscope. Fused into the sides of the vacuum vessel at points where the extended gold leaves touch the glass are two platinum wires, the outer ends of which are earthed. The "clock" acts as follows. The radio-active substance emits a preponderating number of positively electrified particles, so that the leaves become charged and hence extended. On contact with the wires fused into the vessel, this charge is conducted away and the leaves fall together. The process is then repeated, and will continue until all the energy of the radium has been dissipated. This period is extremely long, for 1000 years must elapse before even half the radium has disappeared.-[ED.]

Orffyraeus (whose real name was Johann Ernst Elias Bessler) His last wheel, for he appears to have constructed more than one, (1680-1745) also obtained distinguished patronage for his invention. was 12 ft. in diameter and I ft. 2 in. broad; it consisted of a light framework of wood, covered in with oilcloth so that the interior was concealed, and was mounted on an axle which had no It was examined visible connexion with any external mover. and approved of by the landgrave of Hesse-Cassel, in whose castle at Weissenstein it is said to have gone for eight weeks in a sealed room. The most remarkable thing about this machine is that it evidently imposed upon the mathematician W. J. 'sGravesande, who wrote a letter to Newton giving an account of his examination of Orffyraeus's wheel undertaken at the request of the landgrave, wherein he professes himself dissatisfied with the proofs theretofore given of the impossibility of perpetual motion, and indicates his opinion that the invention of Orffyraeus is worthy of investigation. He himself, however, was not allowed to examine the interior of the wheel. The inventor seems to have destroyed it himself. One story is that he did so on account of difficulties with the landgrave's government as to a licence for it; another that he was annoyed at the examination by 'sGravesande, and wrote on the wall of the room containing the fragments of his model that he had destroyed it because of the impertinent curiosity of 'sGravesande.

The overbalancing wheel perpetual motion seems to be as old as the 13th century. Dircks quotes an account of an invention by Wilars de Honecort, an architect whose sketchbook is still preserved in the Écoles des Chartes at Paris. De Honecort says, Many a time have skilful workmen tried to contrive a wheel that shall turn of itself; here is a way to do it by means of an uneven number of mallets, or by quicksilver." He thereupon gives a rude sketch of a wheel with mallets jointed to its circumference. It would appear from some of the manuscripts of Leonardo da Vinci that he

had worked with similar notions.

season.

Another scheme of the perpetual motionist is a water-wheel which shall feed its own mill-stream. This notion is probably as old as the first miller who experienced the difficulty of a dry One form is figured in the Mathematical Magic (1648) of Bishop Wilkins (1614-1672); the essential part of it is the waterscrew of Archimedes, which appears in many of the earlier machines of this class. Some of the later ones dispense with even the subtlety of the water-screw, and boldly represent a water-wheel pumping the water upon its own buckets.

Perpetual motions founded on the hydrostatical paradox are not uncommon; Denis Papin exposes one of these in the Philosophical Transactions for 1685. The most naïve of these devices is that illustrated in fig. 2, the idea of which is that the larger quantity of water in the wider part of the vessel weighing more will overbalance the smaller quantity in the narrower part, so that the water will run over at C, and so on continually.

D

FIG. 2.

Capillary attraction has also been a favourite field for the vain quest; for, if by capillary action fluids can be made to disobey the law of never rising above their own level, what so easy as thus to produce a continual ascent and overflow, and thus perpetual motion? Various schemes of this kind, involving an endless band which should raise more water by its capillary action on one side than on the other, have been proposed. The most celebrated is that of Sir William Congreve (1772-1828). EFG (fig. 3) is an inclined plane over pulleys; at the top and bottom travels an endless band of sponge, abcd, and over this again an endless band of heavy weights jointed together. The whole stands The capillary action raises the

over the surface of still water. water in ab, whereas the same thing cannot happen in the part ad, since the weights squeeze the water out. Hence, inch for inch, ab is heavier than ad; but we know that if ab were only just as heavy inch for inch as ad there would be equilibrium, if the heavy chain be also uniform; therefore the extra weight of ab will cause the chain to move round in the direction of the arrow, and this will go on continually.

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that it shall draw unto it on a reclined plane a bullet of steel, which, still, as it ascends near to the loadstone, may be contrived to fall through some hole in the plane and so to return unto the place whence at first it began to move, and being there, the loadstone will again attract it upwards, till, coming to this hole, it will fall down again, and so the motion shall be perpetual." The fact that screens do exist whereby electrical and magnetic action can be cut off would seem to open a door for the perpetualmotion seeker. Unfortunately the bringing up and removing of these screens involves in all cases just that gain or loss of work which is demanded by the law of the conservation of energy. A shoemaker of Linlithgow called Spence pretended that he had found a black substance which intercepted magnetic attraction and repulsion, and he produced two machines which were moved, as he asserted, by the agency of permanent magnets, thanks to the black substance. The fraud was speedily exposed, but it is worthy of remark that Sir David Brewster thought the thing worth mentioning in a letter to the Annales de chimie (1818), wherein he states" that Mr Playfair and Captain Kater have inspected both of these machines and are satisfied that they resolve the problem of perpetual motion." The present writer once was sent an elaborate drawing of a locomotive engine which was to be worked by the agency of permanent magnets. He forgets the details, but it was not so simple as the plan represented in fig. 4, where M and N are permanent magnets, whose attraction is screened by the wooden blocks A and B from the upper left and lower right quadrants of the soft iron wheel W, which consequently is attracted round in the same direction by both M and N, and thus goes on for ever.

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One more page from this chapter of the book of human folly; the author is the famous Jean Bernoulli the elder. We N translate his Latin, as far as possible, into modern phraseology. In the first place we must premise the following (see fig. 5). (1) If there be two fluids of different FIG. 4. densities whose densities are in the ratio of G to L, the height of equiponderating cylinders on equal bases will be in the inverse ratio of L to G. (2) Accordingly, if the height AC of one fluid, contained in the vase AD, be in this ratio to the height EF of the other liquid, which is in a tube open at both ends, the liquids so placed will remain at rest. (3) Wherefore, if AC be to EF in a greater ratio than L to G, the liquid in the tube will ascend; or if the tube be not sufficiently long the liquid will overflow at the orifice E (this follows from hydrostatic principles). (4) It is possible to have two liquids of different density that will mix. (5) It is possible to have a filter, colander, or other separator, by means of which the lighter liquid mixed with the heavier may be separated again Construction.-These things being presupposed (says Bernoulli), I thus construct a perpetual motion. Let there be taken in any (if you please, in equal) quantities two liquids of different densities mixed together (which may be had by hyp. 4), and let the ratio of their densities be first determined, and be the heavier to the lighter as G to L, then with the mixture let the vase AD be filled up to A. This done let the tube EF, open at both ends, be taken of such a length that AC: EF2L:G+L; let the lower orifice F of this tube be stopped, or rather covered with the filter or other material separating the lighter liquid from the heavier (which may also be had by hyp. 5); now let the tube thus prepared be immersed to the bottom of the vessel CD; I say that the liquid will continually ascend through the orifice F of the tube and overflow by the orifice E upon the liquid below.

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FIG. 5. Demonstration. Because the orifice F of the tube is covered by the filter (by constr.) which separates the lighter liquid from the heavier, it follows that, if the tube be immersed to the bottom of the vessel, the lighter liquid alone which is mixed with the heavier ought to rise through the filter into the tube, and that, too, higher than the surface of the surrounding liquid (by hyp. 2), so that AC:EF=2L: G+L; but since by constr. AC: EF2L: G+L it necessarily follows (by hyp. 3) that the lighter liquid will flow over by the orifice E into the vessel below, and there will meet the heavier and be again mixed with it; and it will then penetrate the filter, again ascend the tube, and be a second time driven through the upper orifice. Thus, therefore, will the flow be continued for ever.-QE D.

Bernoulli then proceeds to apply this theory to explain the perpetual rise of water to the mountains, and its flow in rivers to the

sea, which others had falsely attributed to capillary action-his idea being that it was an effect of the different densities of salt and fresh water. One really is at a loss with Bernoulli's wonderful theory, whether to admire most the conscientious statement of the hypothesis, the prim logic of the demonstration, so carefully cut according to the pattern of the ancients, or the weighty superstructure built on so frail a foundation. Most of our perpetual motions were clearly the result of too little learning; surely this one was the product of too much. (G. CH.)

PERPETUITY (Lat. perpetuus, continuous), the state of being perpetual or continuing for an indefinite time; in law the tying-up of an estate for a lengthened period, for the purpose of preventing or restricting alienation. As being opposed to the interest of the state and individual effort, the creation of perpetuities has been considerably curtailed, and the rule against perpetuities in the United Kingdom now forbids the making of an executory interest unless beginning within the period of any fixed number of existing lives and an additional period of twenty-one years (with a few months added, if necessary, for the period of gestation). The rule applies to dispositions of personal property (see ACCUMULATION) as well as of real property. There are certain exceptions to the rule, as in the case of limitations in mortmain and to charitable uses, and also in the case of a perpetuity created by act of parliament (e.g. the estate of Blenheim, settled on the duke of Marlborough, and Strathfieldsaye on the duke of Wellington). In the United States the English common-law rule against perpetuities obtains in many of the states; in others it has been replaced or reinforced by statutory rules (see Gray on Alienation, § 42). Charities may be established in perpetuity, and provision may be made for an accumulation of the funds for a reasonable time, e.g. for 100 years (Woodruff v. Marsh, 63 Conn. Rep. 125; 38 Amer. St. Rep. 346). The general tendency of American legislation is to favour tying up estates to a greater extent than was formerly approved.

PERPIGNAN, a town of south-western France, capital of the department of Pyrénées-Orientales, on the right bank of the Têt, 7 m. from the Mediterranean and 42 m. S. by W. of Narbor.ne by rail. Pop. (1906), town, 32,683; commune, 38,898. The north-west quarter of the town is traversed by the Basse, a tributary of the Têt, while to the south it is overlooked by a citadel enclosing a castle (13th century) of the kings of Majorca. The chapel is remarkable as being a mixture of the Romanesque, Pointed and Moorish styles. The ramparts surrounding the citadel are the work of Louis XI., Charles V. and Vauban. The sculptures and caryatides still to be seen on the gateway of the citadel were placed there by the duke of Alva. The cathedral of St Jean was begun in 1324 and finished in 1509. The most noteworthy feature in the building is an immense reredos of white marble (early 17th century) by Bartholomew Soler of

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Barcelona.

In the north of the town commanding the gateway of NotreDame (1481) there stands a curious machicolated stronghold known as the Castillet (14th and 15th centuries), now used as a prison. The buildings of the old university (18th century) contain the library and the museum, the latter possessing the first photographic proofs executed by Daguerre and a collection of sculptures and paintings. Statues of François Arago, the astronomer, and Hyacinthe Rigoud, the painter, stand in the squares named after them.

Perpignan is a fortified place of the first class, and seat of a prefect, a bishop and a court of assizes, and has tribunals of first instance and of commerce, a chamber of commerce, a branch of the Bank of France, a communal college for boys, a school of music and training colleges for both sexes. The higher tribunal of Andovic sits at Perpignan. Trade is in wine, iron, wool, oil, corks and leather.

Perpignan dates at least from the 10th century. In the 11th and 12th centuries it was a capital of the counts of Roussillon. from whom it passed in 1172 to the kings of Aragon. Philip the Bold, king of France, died there in 1285, as he was returning from an unsuccessful expedition into Aragon. At that time it belonged to the kingdom of Majorca, and its sovereigns resided there until, in 1344, that small state reverted to the possession of the

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