Imagens das páginas

would be the more likely to attract attention in England from the circumstance of De Caus having come over to this country in 1612 in the train of the Elector Palatine, and resided here for some years; but still the English nobleman remains, as far as is known, the first person who ever actually constructed a steam-engine, supposing the water-engine seen by Sorbiere to have been such. Twenty years later, as appears from the author's manuscript now in the British Museum, the same idea that had been already published by De Caus, and realised by the Marquess of Worcester, was proposed as his own by Sir Samuel Morland in a work on machines for raising water, written in French, and addressed to Louis XIV.“ ; although the passage was omitted from the book when it was soon afterwards sent to the press. About 1690, Denis Papin, a native of France, but then and for a great part of his life resident in this country, discovered and applied the two important improvements of making the expansive force of the steam act by means of a piston and of producing a reaction of the piston through the condensation of the steam by means of cold; he is also the inventor of the safety-valve, which, however, he only applied in the cooking apparatus called his digester, where steam was employed merely to produce heat, not in any machine where that agent was the moving power. In 1698 Captain Savery contrived the first steam-engine which can be said to have been found practically useful; he employed the principle of the condensation of the steam by cold not to permit the relapse of a piston, as Papin had done, but to effect the elevation of the water directly by allowing it to ascend into the vacuum so produced. From this date steam may be considered to have * Recueil de Machines pour l'Elévation des Eaux, &c.

ranked as an important working power in this country, although Savery's engine was never applied to any other purpose except the raising of water, which, too, it could only effect from a very inconsiderable depth, the vacuum, by means of which it principally operated, ceasing to act as soon as the column of water came to balance an atmospheric column of the same base, in other words, as soon as the water had ascended through the vacuum to the height of about thirty-two feet. About 1711 a much more effective engine was invented by Thomas Newcomen, an ironmonger of Dartmouth, assisted by John Colley, a glazier of the same place, upon Papin's principle, of making the vacuum produced by the condensation of the steam serve for allowing the descent of a piston under its own gravitation and the pressure of the atmosphere. Newcomen's, or the atmospheric engine, as it has been called, soon came to be extensively employed, especially in the mining districts, where water had often to be raised from great depths. Dr. John Theophilus Desaguliers, a clergyman of the Church of England, but of French birth and extraction, in the year 1718 improved Savery's engine (which from its cheapness has for some purposes continued in use to our own day) by substituting the injection of a small current of cold water into the receiver for the old method of dashing the water over the outside of the vessel to effect the concentration of the steam ; and this same improvement—re-discovered, it is said, by himself—was also soon after applied by Newcomen to his engine. About the same time Mr. Beighton contrived to make the machine itself open and shut the cocks by which it received its alternate supplies of steam and water.


At the head of the cultivators of experimental science in England in the latter part of the seventeenth century stands the Honourable Robert Boyle, seventh and youngest son of Richard first Earl of Cork, commonly called the Great Earl. He was born in 1627, and lived till 1691. Boyle was an unwearied observer and collector of facts, and also a voluminous speculator, in physical science; but his actual discoveries do not amount to much. He made considerable improvements on the airpump, originally invented a few years before by Otto von Guericke of Magdeburg, and indeed it may be said to have been in his hands that it first became an instrument available for the purposes of science. The few additions which Boyle made to our knowledge of general principles, or what are called the laws of nature, were almost confined to the one department of pneumatics; he is commonly held to have discovered or established the absorbing power of the atmosphere and the propagation of sound by the air; he proved that element to possess much more both of expansibility and of compressibility than had been previously suspected; he made some progress towards ascertaining the weight of atmospheric air; and he showed more clearly than had been done before his time its indispensableness to the sustentation both of combustion and of animal life. He may be regarded, therefore, along with Torricelli, Pascal, and Guericke, as one of the fathers of pneumatic science -in so far at least as it is concerned with the mechanical

properties of the atmosphere. Boyle also ascertained many particular facts, and arrived at some general, though rather vague, conclusions in chemistry, in the course of his multifarious experiments: the practice of applying one chemical agent as a test for detecting the presence of another was first adopted by him; and he exposed the falsehood of the notion then commonly entertained, that whatever could not be destroyed or changed by fire was to be ranked among the elementary constituents of the natural world. In chemical pneumatics, however, little progress was made either by Boyle or for many years after his day. He conjectured, indeed, that only a portion of the atmosphere was employed in sustaining combustion and animal life; and his fellow-labourer Hooke divined that the element in question is the same with that contained in nitre (namely, what is now called oxygen), and that in combustion it combined with the burning body. But neither of these sagacious conclusions was yet experimentally established.

Robert Hooke, born in 1635, was, till his death in 1702, one of the most devoted cultivators of science in this age. Besides his skill and sagacity as a chemist, he had a remarkable quickness and fertility of mechanical invention, and his speculations ranged over the whole field of natural history and natural philosophy, from the minutest disclosures of the microscope to beyond the farthest sweep of the telescope. His jealous and rapacious temper, and sordid personal habits, which made him an object of general dislike in his own day, have probably somewhat stinted the acknowledgment paid to his merits both by his contemporaries and by posterity; and in fact, of numerous inventions and discoveries to which he himself laid claim, there is scarcely one to which his right has been universally admitted. It is generally allowed, however, that we are indebted to him for the improvement of the pendulum as a measure of time, and for some valuable innovations in the construction of pendulum watches, in particular the application of a spiral spring to regulate the balance. But in his own notion Hooke was the true author of several of the discoveries which have immortalised the greatest of his contemporaries. He disputed partly the originality, partly the truth, of Newton's theory of light; and he even asserted, when the Principia came out, that there was little or nothing there announced on the force and action of gravitation that he had not himself anticipated. He had, indeed, some years before, in a paper printed in the Philosophical Transactions, sketched an hypothesis of the movements of the earth and the other planets on the assumption of the principle of universal gravitation;” but this was a very different thing from the demonstration of the system of the world by Newton on the establishment and accurate measurement of that force. Newton himself eventually admitted that his proposition of the gravitation of the planets being as the inverse square of the distance had been previously deduced from Kepler's discovery of their elliptical orbits by Hooke, as well as by Wren and Halley; but this concession is supposed to have been made rather for the sake of peace than from conviction. *. The first president of the Royal Society, William Brouncker, Lord Viscount Brouncker (of the kingdom of Ireland), who was born in 1620 and died in 1684, * Phil. Trans., No. 101 (for April, 1674).

« AnteriorContinuar »