first forme, and at the second cylinder it received its impression from the second forme. Cowper also improved on this machine, which printed 750 sheets on both sides of the paper per hour. The principle of the first perfecting machine has not been considerably departed from in subsequent machines of the same class, but improved methods have been devised for carrying the sheet from one cylinder to the other and turning it.

Reference, extremely brief and imperfect, has now been made to the origin of two out of the three distinct classes of printing-machines at present in use. These are, first, the single-cylinder machine, printing one side of the sheet at one operation, from a forme lying on a flat bed; second, the double-cylinder or perfecting machine, printing both sides of the sheet at once, also from a forme on a flat bed. The third class comprises the rotary machines, printing both sides, but from a circular forme-the impressing surface, as well as the printing and the inking surface, being cylindrical, and capable of continuous rotation. The machines of the first and second classes are adapted for single sheets of paper; the rotary machines print reels or continuous webs, the portion forming a sheet being severed after printing. It is in this latter class of machines that the greatest improve

ments-amounting almost to a revolution in the art of printing-have been achieved. (For a technical account of the several classes, see Prin ciples and Progress of Printing Machinery, by the present writer, Lond. 1889.) Limitations of space preclude more being given here than a bare list of successive improvements.

The

In 1790, as already mentioned, Nicholson patented a rotary machine, but he never constructed one. In 1813 Bacon and Donkin patented a machine in which the types were fixed on a revolving prism, the ink being applied by a roller, and the sheet of paper wrapped on another prism. machine was a failure, although it embraced an important feature, the inking-roller made of composition. Three years afterwards Cowper patented a method for printing paper for paperhangings and other purposes. This embodied another valuable feature-the taking a cast from the type and bending the cast round a cylinder. It was a far more practical idea than the subsequent one of Rowland Hill, who, to procure a curved printing surface, proposed the use of tapering types to be fixed on the cylinder. In 1848 Applegath invented a machine, the type-cylinder of which was vertical and nearly 6 feet in diameter, around it being placed eight other cylinders,

containing sheets of paper to be printed. These were fed in from a horizontal position, and then brought to the vertical position. In 1857 the Times discarded this machine in favour of one patented by Hoe of New York, very similar in construction, but the cylinders were horizontal. It was found that the complication arising from eight or ten feeders was most objectionable, causing frequent stoppages, excessive waste of paper, and great risk to the machine and the material, while the working cost was heavy. Each of the machines printed on one side only. They were the first machines fitted with flyers '-a device for mechanically delivering or taking off the sheets. It was, however, considered at the Times office that the acme of improvement could only be obtained by constructing a machine simple in its arrangements, capable of printing both sides of the

paper at one operation, and which could print, not single sheets, but continuous webs of paper, thus dispensing with layers-on. There were enormous difficulties in the way of printing, cutting, and delivering the paper, difficulties which the nonprofessional reader could by no means realise. In 1866 a machine of the kind was constructed under the superintendence of Mr J. C. Macdonald, the manager, and Mr Calverley, chief-engineer of the Times. The Walter Press, as this machine was named, has since been slightly improved, but remains practically the same, and is shown in fig. 6. The types are stereotyped by means of a papier-maché mould, which, being bent inside a hollow cylinder, produces, when cast, a stereotype which fits on the printing-cylinder of the machine. The paper, unwinding from the reel, first passes between damping-cylinders, then over the printing

PRINZENRAUB

have been brought to their present degree of perfection, that they give far superior results to those from presses-their impression is stronger, more solid, and more uniform, and the sheets can be laid on them with a precision unattainable with hand-presses. Paper is not now made spongy and stretchable by being wetted, and the result of working it dry is that the type is brought up with greater brightness, and the delicate lines of engrav. ings are printed finer, clearer, and cleaner. Improvements in ink-making have much conduced to this desirable result. Paper has been produced for book printing with a specially prepared surface, which admits of a far more excellent impression than that formerly procurable. The soft blanket has been discarded, and the packing or covering of the cylinder is now generally as hard as it can be got. The aggregate results of these alterations may be seen by a comparison of the present issues of an illustrated newspaper with those of fifty years ago. Up to about 1840 there was actually no press strong enough to properly print a woodcut of 48 square inches in superficies; now, woodcuts of 2000 square inches, or 50 inches by 40, are printed in the most perfect manner. The coloured supplements of the pictorial journals are often admirable reproductions of works of high art; it is within the memory of persons of middle age that the first crude attempts were made to print such pictures. BIBLIOGRAPHY.-Historical: In addition to the works referred to in the text may be mentioned Karl Faulmann, Illustrierte Geschichte der Buchdruckerkunst (Vienna, 1882), his Die Erfindung der Buchd. nach der neuesten Forschungen (Vienna, 1891); Theo. de Vinne, The Invention of Printing (New York, 1877); and Van der Linde, Geschichte der Erfindung der Buchd. (3 vols. Berlin, 1886). There is no complete history of printing in the English language, but in Bigmore and Wyman's Bibliography of Printing (3 vols. 1880-86) some of the

inost useful books will be found under the names of Ames, Arber, Blades, Dibdin, Herbert, Hansard, Humphreys, Hessels, Luckombe, Ottley, T. B. Reed, Sotheby, Timperley, and Watson.

Practical.-Southward, Practical Printing (2 vols. 3d ed. 1887), and Printing Machines and Machine Printing (1888); Waldow, Illustrierte Encyklopadie der Graphischen Kunste (Leip. 1884); Desormes, Notions de Typographie (Paris, 1888); F. J. F. Wilson, Printing Machines (3d ed. 1885); F. J. Jacobi, Printing (1890); The American Dictionary of Printing and Bookmaking (1891-94); Ringwalt, American Encyclopedia of Printing (New York, 1871). Besides, a multitude of small yet useful books have been written on separate branches, and for the use of professional students of the art. See also the articles BIBLIA PAUPERUM, BOOK, BOOK-CLUB, ILLUSTRATION, LITHOGRAPHY, PAPER, PRESS (FREEDOM OF THE), PROOFS, STEREOTYPING, TYPES.

Prinzenraub. See ALTENBURG.
Prior. See MONASTERY, ABBOT.

Prior, MATTHEW, was born 21st July 1664. Some doubt prevails as to his birthplace; but the bulk of the evidence points to Wimborne Minster in East Dorset. His father is said to have been a joiner, who, coming to London, probably to educate his son, took up his abode in Stephen's Alley, Westminster. Young Prior went to Westminster School, then under the redoubtable Dr Busby. His father died, and, his mother being unable to pay his schoolfees, he fell into the care of his uncle, a vintner in Channel (now Cannon) Row, who took him into the bar to keep accounts. Here his familiarity with Horace and Ovid attracted the attention of Charles, Earl of Dorset, and other visitors to the Rhenish Wine House, with the result that he returned to Westminster, his uncle finding him in clothes, and Dorset in books. At Westminster he formed a lifelong friendship with the two sons of the Honourable George Montague, the elder of whom afterwards became Earl of Halifax. In order to follow his

friends to Cambridge, Prior, against Lord Dorset's wish, accepted a scholarship from the Duchess of Somerset at St John's College. He was admitted Bachelor in 1686, and in the following year wrote with Charles Montague the clever parody of Dryden, entitled The Hind and the Panther transvers'd to the Story of the Country-mouse and the City-mouse, which, according to tradition, greatly annoyed Dryden. In April 1688 Prior obtained a fellowship; and his composition of the yearly college tribute to the Exeter family, a rhymed excursus upon Exodus, iii. 14, led to his going to Burleigh as tutor to Lord Exeter's sons. Lord Exeter shortly afterwards removed to Italy, and Prior applied (through Fleetwood Shepherd) to his former patron Dorset for advancement. He was, being then twenty-six, made secretary to Lord Dursley, afterwards Earl of Berkeley, then going as ambassador to the Hague. In Holland Prior remained some years, finding especial favour with King William. In 1697 he brought over the Articles of Peace at the treaty of Ryswick; and, after being nominated Secretary of State for Ireland, he was made secretary in 1698 to the Earl of Portland's embassy to France, continuing this office under the Earl of Jersey. In this capacity he found favour both with Anne and Louis XIV. In 1699 he became an under-secretary of state, the university of Cambridge made him an M. A., and he succeeded Locke as commissioner of trade and plantations. In 1701 he entered parliament as member for East Grinstead. Under Anne he joined the Tories, and in 1711 was employed in the preliminaries of the peace of Utrecht, going to Paris as ambassador in the following year. With the queen's death in 1714 came the triumph of the Whigs, and in 1715 Prior, returning to England, was impeached and imprisoned. In 1717 he was excepted from the Act of Grace, but was, none the less, subsequently discharged. The remainder of his life was passed chiefly at Down-Hall in Essex, a country-house purchased partly with the profits of a subscription edition of his poems and partly with the assistance of his friend Lord Harley, at whose seat of Wimpole he died, 18th September 1721, being then in his fifty-eighth year. He was buried ated with his bust by Antoine Coysevox, given to in Westminster Abbey, under a monument decorhim by Louis XIV. His portrait was painted by Richardson (National Portrait Gallery), by Belle (St John's College), Kneller, Dahl, and others.

But

Of Prior's abilities as a diplomatist there are diverse opinions. Pope sneered at them. Bolingbroke and Swift extolled them; and it is stated that the archives at Paris show him to have been far abler and more resourceful than is generally supposed. As a poet, in which capacity he is now remembered, he holds a unique position. Without much real sentiment or humanity, his verses have a wit, a grace, a neatness and a finish, which link him to the lighter Latin poets on the one hand, and to the best French writers of familiar verse on the other. Cowper praised his 'easy jingle,' Thackeray his good sense, his happy easy turns and melody.' He collected his poems, described by himself as consisting of Publick Panegyrics, Amorous Odes, Serious Reflexions, or Idle Tales' (many of which had been contributed to Dryden's and other miscellanies), in 1709, and again, in extended form, in 1718. By this latter issue he made £4000. His more ambitious pieces, Solomon on the Vanity of the World and a paraphrase of the old ballad of the Nut Brown Maid, are not now thought to be his best, although they had considerable popularity with the readers of the 18th century. But a third long poem, Alma; or, the Progress of the Mind, an imitation of Butler, is full of wit and waywardness. His Tales resemble the French contes too much in their objectionable

qualities to be palatable to the English taste. He survives mainly by his purely playful efforts, his lyrics and his epigrams, not a few of which are unsurpassable. In the kind of piece known to the French as vers d'occasion he is unrivalled, and his beautiful stanzas to A Child of Quality have been as fortunate as Gray's Long Story in setting the tune to a host of versifiers. In 1740, long after his death, two volumes were published, one containing alleged Memoirs, in which there is little of his, and the other a number of posthumous verses, among which are some of his best. These are included in Evans's two-volume edition of 1779. Thackeray wrote admirably of Prior in his English Humourists (1853). The latest information respecting him, including some hitherto unpublished data, is to be found in his Selected Poems, edited by the writer of this notice (Parchment Library, 1889), and in an article by Mr G. A. Aitken in the Contemporary Review for May 1890.

Priscian (Lat. Priscianus), surnamed CÆSARIENSIS, born or educated in Cæsarea, is in point of reputation the first of Latin grammarians; his treatise was in universal use as a text-book during the middle ages. Priscian flourished in the beginning of the 6th century: Paulus Diaconus calls him a contemporary of Cassiodorus (468-562 A.D.). He taught Latin at Constantinople, and enjoyed a government salary. The work which has preserved his name is his Commentariorum Grammaticorum Libri XVIII. The first sixteen books treat of the

different parts of speech; the remaining two, of syntax. The work shows great learning and good sense, and contains quotations from many Greek and Latin authors no longer extant. Priscian also wrote six smaller grammatical treatises, and two hexameter poems of the didactic sort, De Laude Imperatoris Anastasii and a free translation of the Periegesis of Dionysius. The best edition of the grammatical works is that by Hertz and Keil in Keil's Grammatici Latini, vols. ii. and iii. (1855-60); of the poems, by Bährens, in Poeta Latini Minores, vol. v. (1883).

Priscillian, the chief propagator of the doctrines professed by the sect known from his name as Priscillianists. They spread widely in Spain during the last third of the 4th century, and lingered there till the middle of the 5th century.

The first seed of their doctrines is said to have been carried into Spain by a Memphian named Marcus, whose earliest disciples were Agape, a Spanish lady, and Helpidius, a rhetorician. Priscillian was a man of noble birth, pious and well educated; and his eloquence and nobility of character soon gathered round him a group of devoted followers, including two bishops, Instantius and Salvianus. From their hands he received episcopal ordina tion, and he established his see at Avila (Abila). Hyginus, bishop of Cordova, was the first to take alarm, but his measures were so gentle that he himself was covered with reproaches by the ultra-orthodox and fanatical. Priscillian's most determined enemies were Idacius, bishop of Emerita (Merida), and Ithacius, bishop of Sossuba. He was condemned and excommunicated at the synod of Saragossa (381), with three others of the leaders of the party. They next went to Rome to clear themselves before the pope, but were denied audience, and at Milan on the return journey they met as little sympathy from Ambrose. Under the vacillating rule of Gratian, however, they prospered, but their hopes were dashed to the ground by the usurpation of Clemens Maximus. From the judg. ment of the synod of Bordeaux (384) Priscillian appealed like Paul to Cæsar, and was at length summoned to appear at Treves. Martin of Tours was in favour of tolerant measures, but after his

PRISONERS OF WAR

departure the fanatical party prevailed, and Priscillian, with others of the party, was condemned and put to death-the first who suffered death for heresy (385). Many Priscillianists recanted after the synod of Toledo (400), and soon after that of 447 they disappear altogether. Their doctrines contained Manichæan and Gnostic elements, strange cosmical speculations based on primitive dualism, the doctrine of emanations and astrological fatalism. They practised rigid asceticism, and eschewed marriage and the use of animal food. One damning blot on their morals was that absolute veracity was only obligatory between themselves. Graver charges still were made against their morality; but it should be remembered that the only accounts we have are those of bitter enemies, and their principles, originally obscure enough, have been made darker by a cloud of calumny. If the Priscillianists violated the laws of nature,' says Gibbon, it was not by the licentiousness but by the severity of their lives.'

See Mansel's Gnostic Heresies and Neander's Church History; also Mandernach's Geschichte des Priscillianismus

(Treves, 1851). Schepps claims to have discovered some of his writings; these he edited in vol. xviii. of the Corpus Scriptorum Ecclesiasticorum Latinorum (Vienna, 1888).

Prism, in Geometry, a solid figure which can of plane figures (triangles, quadrilaterals, &c.) be most easily conceived of if we imagine a number exactly similar in form and size to be cut out of other, and then the whole pile to become one body. paper or any thin plate, and piled one above the It will thus be seen that the top and bottom of the prism are similar, equal, and parallel to each other, and that the sides are plane figures, rectangular if the prism be 'right' (i.e. if in the above illustration and rhomboidal if the prism be oblique' (i.e. if the the pile of plane figures be built up perpendicularly), pile slope to one side); but under all circumstances the sides of a prism must be parallelograms. The top and bottom faces may be either triangles, sort, or figures of five, six, seven, &c. sides, provided squares, parallelograms, or quadrilaterals of any only both are alike; and the number of sides in the plane figure which forms the top or bottom of course determines the number of faces of the prism; thus, in a triangular prism, there are five faces in all (three sides and two ends); in a quadrangular prism, six faces (four sides and two ends), &c. If two prisms, one being right,' and the other oblique,' have their bases of equal area, and be of the same vertical height, their solid content is the same, and is found by multiplying the area of the base by the vertical height. The parallelopiped is a quadrangular prism, and the cube is a particular case of the parallelopiped.

PRISM, in Optics, is a triangular prism of glass or other transparent substance, its two ends being isosceles triangles, and having most frequently a very acute vertical angle, which gives the prism the appearance of a long wedge. The prism is a most important instrument in experiments on the refraction of light, and, in the hands of the most eminent optical philosophers, has been the means of largely adding to the science of optics. See OPTICS, REFRACTION, SPECTRUM.

Prisoners of War are those who are captured from the enemy during naval or military operations. By the laws or recognised principles of war, the entire people of a vanquished town, state, or nation become the absolute property of the victors. In ancient times the treatment of prisoners of war was very severe. In the Greek wars it was no uncommon thing to put the whole adult male population of a conquered state to the sword, while the women and children were enslaved. Although the putting to death of prisoners became less frequent, they and their families were commonly reduced to slavery to as recent a period as the 13th