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POG instruction. For a short time he endeavoured to carry out the constitution, but resigned office in April, taking his place in the new parliament for Naples. After the tragical events of the 15th May, 1848, Poerio became one of the leaders of the opposition, and maintained his post until the forcible subversion of parliamentary government, March 12, 1849. On the 19th July of the same year he was arrested, with many hundreds of others, on a double charge of being a leader in the secret society of the Unita Italiana, and of having fought on the barricades on the 15th May. The evidence against him was made up of forgery and perjury of the most transparent character, and the horrible sufferings endured by the forty-two prisoners associated with him have been made known in the memorable letters of Mr. Gladstone. He was brought to a mock trial, and sentenced to twenty-four years' imprisonment in chains. He suffered a portion of this sentence, aggravated by nameless barbarities and illegalities, at Nisida, Ischia, and Montesarchia, until 1859, when, with about sixty others, he was placed on board an American vessel, bound for New York. By a stratagem whose success may be deemed romantic, the exiles obtained possession of the vessel and brought her into Cork harbour. They were hospitably received by the English people, and shortly afterwards Poerio found his way to Turin, and was elected to the first Italian parliament. He holds the office of vice-president of the chamber of deputies, though he very seldom presides. One of his earliest acts was to vote for the cession of Nice and Savoy; and he has invariably supported the minister of the day, whoever might be in power.—F. M. W.  POGGIO. See.  POILLY,, an eminent French engraver, was born at Abbeville in 1622. He studied at Paris under P. Daret, and afterwards at Rome under C. Bloemart. F. Poilly was a most industrious engraver. About four-hundred prints bear his name. In a large proportion of these he was assisted by his pupils, but Nagler gives a list of one hundred and seven engraved wholly by him. His prints are executed entirely by the graver. His line is firm and neat, but somewhat hard; his drawing pure. His best plates are the San Carlo Borromeo of Mignard; Raphael's large Holy Family in the Louvre, and Vierge au Berceau; and Guido's Flight into Egypt. F. Poilly died in 1693.—J. T—e.  POILLY,, son of Nicolas Poilly, born at Paris in 1669, learned engraving of his father, but completed his studies at Rome. He drew well, and was skilful in expression. Unlike his uncle, he used the graver mainly in finishing his plates. He died at Paris in 1728.—J. T—e.  POILLY,, born at Abbeville in 1626, was the younger brother and pupil of François Poilly, whose manner he adopted, but with inferior success. He engraved several of the works of Charles Le Brun and S. Bourdon, and portraits of Louis XIV. and his family. He died at Paris in 1696 —J. T—e.  POINSINET DE SIVRY,, dramatist and translator, was born in 1733 at Versailles, and received his education at the college de la Marche. He was the author of three tragedies—"Briseis," "Ajax," and "Cato of Utica" and he also translated the works of Anacreon, Bion, and Moschus, Pliny's Natural History, the comedies of Aristophanes, and the fragments of Menander and Philemon.—W. J. P.  POINSOT,, a distinguished French mathematician and writer on mechanics, was born in Paris on the 3d of January, 1777, and died there on the 5th of December, 1859. From 1794 to 1797 he was a student in the Polytechnic school, in which he afterwards held successively the appointments of professor of analytical mechanics from 1809 till 1816, and of examiner from 1816 till 1825. In 1813 he became a member of the Academy of Sciences. He was professor of mathematics in the Lycée Bonaparte and a member of the superior council of public instruction. In 1852 he was created a senator by the Emperor Napoleon III. He conferred a great benefit on the science of mechanics by introducing into it systematically the idea of a "couple"—that is, a combination of two forces equal and opposite to each other, but not directly opposed, tending to produce rotation, and incapable of being balanced except by an equal and opposite couple—and showing how such couples are compounded and resolved by laws analogous to those of the composition and resolution of single forces, and how their properties may be applied to the solution of all kinds of statical and dynamical problems, especially such as have reference to rotation, or to tendencies to rotate. This idea he first put forth in a treatise on statics, published in 1804; and in a long series of subsequent writings he developed it in various ways.—W. J. M. R.  POIRET,, the famous mystic, was born at Mentz in 1646. After a course of study at Heidelberg and Basle, he became in 1672 pastor at Amveil in the duchy of Deux Ponts. Here he published his "Cogitationes rationales de Deo, Anima, et Malo"—a work based on Cartesian principles, and which he was obliged to defend against the sharp assaults of Bayle. In 1676, in consequence of the advance of the French army, he retired to Hamburg, where he became acquainted with Madame Bourignon, and immediately became her ardent disciple and the fervent exponent of her views. Like many men who renounce a system with which they had identified themselves, he began his new career by vilifying the philosophy of Des Cartes. His first book was his "De Economia Divina," in seven volumes. His favourite principle is abstraction; that is, the putting out of reason as a guide, and the adoption instead of an inner illumination, or species of clairvoyance, conferred on the initiated. Towards the conclusion of his life he settled at Rheinsberg, where he died in 1719. He wrote also "De Eruditione Triplici," &c. Poiret's reveries are inferior to the "divine visions" of Böhmen, and they have to a great extent passed into oblivion.—J. E. <section end="763H" /> <section begin="763I" />POISSON,, one of the greatest of French mathematicians, was born at Pithiviers on the 21st of June, 1781, and died in Paris on the 25th of April, 1840. The orphan child of a "juge de paix," or local magistrate, he was educated through the liberality of his uncle, Lenfant, a surgeon at Fontainebleau, and he there began his mathematical studies under Billy. From 1798 till 1800 he was a student at the Polytechnic school, where his great abilities attracted the favourable notice of Hachette (q.v.), and obtained for him rapid advancement. From 1800 to 1802 he was an assistant professor at the Polytechnic school, and in 1802 he was appointed to the professorship of analytical mechanics, which he held until 1815. From that year until his death he held the office of examiner in the Polytechnic school. He was also professor of mechanics in the Faculty of Science, and a member of the Board of longitude. In 1812 he became a member of the Institute. The Emperor Napoleon I. conferred on him the rank of baron; and in 1837 he was made a peer of France. His writings comprise more than three hundred memoirs on mathematical, mechanical, and physical subjects, which appeared in the Transactions of scientific bodies, and in the scientific journals. One of his most remarkable discoveries was the demonstration of the invariability of the major axes of the planetary orbits. His "Traité de Mécanique"' is a standard work for all students of that science in its highest form. In his "Théorie Nouvelle de l'Action capillaire" he investigates in the most profound and exact manner the consequences of certain suppositions as to the molecular constitution of bodies, which consequences he developed further in his investigations on the theory of the elasticity of solid bodies. In his "Théorie Mathematique de la Chaleur" he reinvestigates in a more general way a subject which was first put into a mathematical shape by Fourier—that of the conduction of heat. Independently of the physical questions to which they relate, his works possess the highest interest and value in a purely mathematical point of view, owing to the new and powerful methods of investigation which they contain.—W. J. M. R. <section end="763I" /> <section begin="763J" />POISSON,, entered the Oratorio in 1660, and died at Lyons, May 5, 1710. He travelled in Italy, and was much admired for his talent and learning. He was a great student of mathematics, especially of the works of his friend Descartes. In 1706 he published a collection of Councils of the Church, &c. He also wrote "Remarks on some of Descartes' writings;" "An account of a journey to Italy," &c.—B. H. C. <section end="763J" /> <section begin="763Zcontin" />POITIERS,, was the daughter of the count of St. Vallier, and was born in 1500. Her father having incurred the penalties of treason by abetting the escape from France of the Constable de Bourbon, was condemned to death. Diana, however, interceded with Francis I. for his life, and such was the impression which her beauty and captivating address made upon that susceptible monarch that he at once pardoned the count, received his daughter into favour, and built for her the châteaux of Auct and Chambord. Diana was subsequently married to De Breze, grand seneschal of Normandy. After his death she captivated Henry II., who in 1548 created her Duchess of Valentinois, and though she had obtained the mature age of forty while the king was only eighteen, she gained such a complete ascendancy <section end="763Zcontin" />