456 P N P N declaring and interpreting the laws of religion, which involved such important social matters as marriage and testamentary dispositions ; but this function was declara tory and not magisterial ; the state gave no executive power to the pontiffs, save only that the pontifex maximus exercised disciplinary authority over those priestly persons who stood under his paternal power. The pontiffs, who held office for life, originally filled up the vacancies in their number by cooptation, but as early as 212 B.C. the head of their college was named by the voice of the people, and in 104 B.C. the choice of the members of the priestly colleges was also transferred to comitia of a peculiar constitution. The number of pontifices was gradually enlarged, first to nine and then, under Sulla, to fifteen, and the emperors exercised the right of adding supernumeraries at will. PONTINE MARSHES. See LATIUM, vol. xiv. p. 343. j PONTOISE, a commercial town of France, at the head ] of an arrondissement of the department Seine-et-Oise, 18 miles by rail north-west of Paris, picturesquely situated on the right bank of the Oise where it is joined by the | Viosne, and at the intersection of the railway from Paris to Dieppe by Gisors with that of the valley of the Oise. | The traffic on the main river is large, and the tributary drives numerous mills. Of the many convents and j churches that used to exist in the town two only remain : St Maclou, a church of the 12th century, was altered and restored in the 15th and 16th centuries by Pierre Lemer- , cler, the famous architect of St Eustache at Paris; and Notre Dame, of the close of the 16th century, contains the j toinb of St Gautier (13th century). Grain and flour are j the principal staples of the trade of Pontoise ; the popula tion in 1881 was 6675. Pontoise existed in the time of the Gauls as Briva Isarse (i.e., Bridge of the Oise). The Romans made it the seat of forges dedi cated to Vulcan, and thus the district came to be distinguished as Pagus Vulcanius or the Vexin. Pontoise was destroyed by the Normans in the 9th century, united with Normandy in 1032, and acquired by Philip I. in 1064. Lying on the borders of the two states it often passed from one to the other. The English took it in 1419, and again in 1436. In 1441 Charles VII. took it by storm after a three months siege. After belonging to the count | of Charolais down to the treaty of Conflans, it was given as a j dowry to Jeanne of France when she was divorced by Louis XII. The parlement of Paris several times met in the town ; and in 1561 the states -general convoked at Orleans removed thither after ] the death of Francis II. During the Fronde it offered a refuge to Louis XIV. and Mazarin. Henry III. made it an apanage for i his brother the duke of Anjou. At a later period it passed to the duke of Conti. Down to the Revolution it remained a monastic town. Philip the Bold, founder of the house of Burgundy, the architects Pierre and Jacques Lemercier, and Tronson-lJucondray, one of the defenders of Marie Antoinette, are among the natives of Pontoise. PONTOON. Pontoons are vessels employed to sup port the roadway of floating bridges. They may be either open or closed, heavy and only movable when floated, or light enough to be taken out of the water and transported overland, as when required to form part of the equipment of an army in the field. From time immemorial floating bridges of vessels bearing a roadway of beams and planks have been employed to facilitate the passage of rivers and arms of the sea. Xerxes crossed the Hellespont on a double bridge, one line supported on three hundred and sixty, the other on three hundred and fourteen vessels, anchored head and stern with their keels in the direction of the current. Darius threw similar bridges across the Bosphorus and the Danube in his war against the Scythians, and the Greeks employed a bridge of boats to crass the river Tigris in their retreat from Persia. Float ing bridges have been repeatedly constructed over rivers in Europe and Asia, not merely temporarily for the passage of an army, but permanently for the requirements of the country ; and to this day many of the great fivers in India are crossed, on the lines of the principal roads, by floating bridges, which are for the most part supported on boats such as are employed for ordinary traffic on the river. But light vessels which can be taken out of the water and lifted on to carriages are required for transport with an army in the field. Alexander the Great occasionally carried with his army vessels divided into portions, which were put together on reaching the banks of a river, as in crossing the Hydaspes ; he is even said to have carried his army over the Oxus by means of rafts made of the hide tents of the soldiers stuffed with straw, when he found that all the river boats had been burnt. Cyrus crossed the Euphrates on stuffed skins. In the 4th century the emperor Julian crossed the Tigris, Euphrates, and other rivers by bridges of boats made of skins stretched over osier frames. In the 17th century the Germans employed timber frames covered with leather as pontoons, and the Dutch similar frames covered with tin ; and the practice of carrying about skins to be inflated and employed for the passage of troops across a river, which was adopted by both Greeks and Eomans, still exists in the East, and has been introduced into America in a modified form, india-rubber being substituted for skins. Pontoons have been made of a variety of forms and of almost every conceivable description of material available for the purpose of combining the two essential qualities of transportability over land and power of support in water. As these qualities are not only distinct but conflicting, one of them has been frequently sacrificed to the other. Thus history records many instances of bridges having failed because incapable of supporting all the weight they were called on to bear, or of resisting the force of the current opposed to them ; it also records instances of important strategical operations being frustrated because the bridge equipment could not be brought up in time to the spot where it was wanted. Numerous expedients for lightening the equipment have been suggested, in America more particularly ; but the proposers have not always re membered that if a military bridge is intended to be carried with an army it is also intended to carry the army, with its columns of infantry and cavalry, its numerous waggons, and its ponderous artillery, and it ought to do so with certainty and safety, even though a demoralized rabble should rush upon it in throngs. Pontoons have been made of two forms, open as an undecked boat, or closed as a decked canoe or cylinder. The advantage claimed for the closed pontoon is that it cannot be submerged by the river, but only by having to bear a greater load than its buoyancy admits of ; the disadvantages are that it is difficult to make and keep water-tight, it requires special saddles for the support of the baulks which carry the roadway, and it cannot be conveniently used as a row-boat. During the Peninsular War the English employed open bateaus, as did and still do all the other European nations ; but the experience gained in that war induced the English to abandon the open bateau ; for if large it was very difficult to transport across country, and if small it was only suited for tranquil streams, being liable to fill and sink should the river rise suddenly or become disturbed by the wind. Thus closed pontoons came to be introduced into the British army. General Colleton devised the first substitute for the open bateau, a buoy pontoon, cylindrical with conical ends and made of wooden staves like a cask. Then General Pasley introduced demi-pontoons, like decked canoes with pointed bows and square sterns, a pair, attached sternwise, forming a single " pier " of support for the roadway ; they were constructed of light timber frames covered with sheet
copper and were decked with wood; each demi-pontoou