DENIS PAPIN (1647 -c. 1712), French physicist, and one of the inventors of the steam-engine, was a native of Blois, where he was born in 1647. In 1661 or 1662 he entered upon the study of medicine at the university of Angers, where he graduated in 1669, with the intention apparently of settling as a practising physician in that city. Some time prior to 1674 he removed to Paris and assisted Huygens in his experiments with the air-pump, the results of which (Experiences du Vuide) were published at Paris in that year, and also in the form of five papers by Huygens and Papin jointly, in the Philosophical Transactions for 1675. Shortly after the publication of the Experiences, Papin, who had crossed to London hoping to find some congenial employment, was hospitably received by Boyle, and gave him some assistance in his laboratory and with his writings; about this time also he introduced into the air-pump the improvement of making it with double barrels, and replacing by the two valves the turn-cock hitherto used. He is said, moreover, to have been the first to use the plate and receiver, which are organs of capital importance in the modern form of the instrument. Subsequently he invented the condensing-pump, and in 1680 he was admitted, on Boyle's nomination, to the Royal Society. In the following year he communicated to the Society an account of his famous steam " digester, or engine for softening bones," afterwards described in a tract published at Paris, and entitled La maniere d'amollir les os et de /aire couire toutes sortes de viandes en fort pen de terns et a pen de frais, avec une description de la marmite, ses propríétés et ses usages. In this instrument the principle of the safety-valve was applied for the first time. After some further experiments with the digester he accepted an invitation to Venice to take part in the work of the recently founded Academy of the Philosophical and Mathematical Sciences; here he remained until 1684, when he returned to London and received from the Royal Society an appointment as " temporary curator of experiments, " with a small salary. In this capacity he carried on numerous and varied investigations, in the course of which he discovered a siphon acting in the same manner as the " Sipho Wirtembergicus" (Phil. Tr., 1685), and also constructed a model of an engine for raising water from a river by means of pumps worked by a water-wheel driven by the current. In November 1687 he was appointed to the chair of mathematics in the university of Marburg, and here he remained until 1696, when he removed to Cassel. From the time of his settlement in Germany he carried on an active correspondence with Huygens and Leibnitz, which is still preserved, and in one of his letters to Leibnitz, in 1698, he mentions that he is engaged on a machine for raising water to a great height by the force of fire; in a later communication he speaks also of a little carriage he had constructed to be propelled by this force. Again in 1702 he wrote about a steam " ballista," which he anticipated would " promptly compel France to make an enduring peace." In 1705 Leibnitz sent Papin a sketch of Savery's engine for raising water, and this stimulated him to further exertions, which resulted two years afterwards in the publication of the Ars nova ad aquam ignis adminiculo efficacissime elevandam (Cassel, 1707), in which his high-pressure boiler and its applications are described (see STEAM-ENGINE). In 1707 he resolved to quit Cassel for London, and on September 24th of that year he sailed with his family from Cassel in an ingeniously constructed boat, propelled by paddle-wheels, to be worked by the crew, with which he apparently expected to reach the mouth of the Weser. The expedition, however, came to an ignominious end at Münden, where the vessel was confiscated at the instance of the boatmen, who objected to the invasion of their exclusive privileges in the Weser navigation. Papin, on his subsequent arrival in London, found himself without resources and almost without friends; various applications through Sloane to the Royal Society for grants of money were made in vain, and he died in total obscurity, pro-bably about the beginning of 1712.

The published writings of Papin, besides those already referred to, consist for the most part of a large number of papers, principally on hydraulics and pneumatics, contributed to the Journal des Savans, the Nouvelles de la Mepublique des Leltres, The Philosophical Transactions, and the Acta Eruditorum; many of them were collected by himself into a Fasciculus dissertationum (Marburg, 1695), of which he published also a translation into French (Rccueil de diverses pieces toucliant quelques nouvelles machines (Cassel, 1695). His correspondence with Leibnitz and Huygens, along with a biography, has been published by Dr Ernst Gerland (Leibnizen's und Huygens' Briefwechsel mit Papin, nebst der Biographic Papin's, Berlin, 1881).