PRACTICAL ESSAY, &c. CHAP. I. ON NATURAL PHILOSOPHY. MECHANICS, definition of :—connected with the Arts of Life-allied to Geometry-History of Mechanics: what included under. Centrifugal and Centripetal forces-Mechanical Powers: Lever-Wheel and Axle -Pulley-Inclined Plane-Wedge-and the Screw. Writers on Mecha nics: Keill-Wood-Parkinson-Ferguson. IN a course of natural philosophy, it is usual to place Mechanics at the head, because much of every other department depends upon the right apprehension of the theory of this. Mechanics may be defined "the science which treats of the laws of the equilibrium and motion of solid bodies; of the forces by which bodies, whether animate or inanimate, may be made to act upon one another; and of the means by which these may be increased to almost any degree. As the practical part of this science is closely connected with the arts of life, and particularly with those which existed even in the rudest ages of society, the construction of machines must have been understood and practised in some way or other, long before any theory could have been invented, or even thought of. Hence, at a very early period, we read of the use of the lever, the pulley, the capstan, and other simple machines, long before the principles of their action could have been investigated. In the remains of Egyptian architecture, there are the most striking marks of mechanical invention. The elevation of ponderous, and almost immense masses of stone, to very great heights, seems to have required an accumulation of force and mechanical power with which modern architects and mechanics are unacquainted. The theory of Mechanics, next to that of Geometry, is reckoned the most certain: generally speaking, it proposes for consideration, Time and Force, or Power; and the following properties of matter, viz. extension, figure, impenetrability, mobility, and inertia. The application of this science to the various practical purposes in human life, leads to many branches of inquiry; such as the nature of machinery, the advantages, and disadvantages of different materials, the effects of friction, &c. All which will merit the attention of the student in Natural Philosophy, though the limits of our work will not permit us to do more than take a cursory notice of them, and then refer to works of authority in which the subjects are discussed at large. The first traces that we have of auy thing like theory in this branch of science, is in a work of Archimedes on " Equiponderants," in which he considers a balance supported on a fulcrum, having a weight in each scale; and taking as a fundamental principle, that when the two arms of the balance are equal, the two weights supposed to be in equilibrio, are also equal, he shews, that if one of the arms be increased, the weight applied to it must be proportionally diminished. Hence he arrives at the general conclusion, that two weights, suspended to the arms of a balance of unequal length, and remaining in equilibrio, must be reciprocally proportional to the arms of the balance. This is the first trace, any where to be met with, of a theoretical investigation of mechanical science. Archimedes did not, however, stop here; he advanced, from step to step, till he was enabled to find the centre of gravity of various bodies; and to him we are indebted for the theory of the inclined plane, the pulley, and the screw, besides the invention of several machines, of which, unfortunately, scarcely any thing is now known. From the time of Archimedes till the commencement of the sixteenth century, little was done to advance the theory of mechanics. About this period, Stevinus, to whom we have before referred, made many discoveries in the laws of equilibrium, which the great Galileo carried much farther. This philosopher, who flourished at the end of the sixteenth, and beginning of the seventeenth centuries, laid the foundation of almost all the discoveries which have succeeded each other, for more than two centuries. He investigated the laws of accelerating forces; and shewed the nature of the curve, which is described by a projectile: he inferred, from observation, the isochronism of the vibrations of a pendulum, and the principle was soon applied to the regulation of chrono meters. The laws of collision, another branch of mechanics, were investigated nearly at the same time in England by Wren and Wallis, and in France by Huygens. Next to the discoveries of Archimedes and Galileo, those of Huygens hold the third place in the order of time, and may be ranked among the greatest benefits that have been conferred on science. His investigations of the cycloid, and his doctrine of central forces, were the immediate foundation of Sir Isaac Newton's improvements. Hooke was great as a mechanician; his inventions were numerous, and very important in the history of mechanics. Dr. Barrow, in his lectures, treated at large of the composition of motion, and other mechanical subjects. He was professor of mathematics at Cambridge, an office which he willingly resigned, to make way for the immortal Newton, whose whole life was a life of discovery: to say nothing of the other topics which he explained and illustrated, his theory of gravitation, and the mechanics of the universe, are developed in his Principia, first published in 1687. He considers in that work the subject in its utmost extent; and contein plates every conceivable variation of moving force, and determines the motion resulting from its actions. His first application of these doctrines was to explain the celestial motions; and the magnificence of this subject caused it to occupy, for some time, the whole attention of mathematicians. But the same work contained propositions equally conducive to the improvement of common mechanics, and to the complete understanding of the mechanical actions of bodies. Sir Isaac Newton lived to a great age, and had, says Fontenelle," the singular happiness of obtaining, during life, all the credit and consideration to which his sublime researches, and his fortunate discoveries, entitled him. All men of science, in a country which produces so many, placed Newton, by a kind of acclamation, at their head." The Bernoullis on the continent were successfully pursuing the same studies with the illustrious English philosopher, and the general laws of mechanics were very elegantly investigated, and applied by these contemporary philosophers, while Machin, Cotes, Halley, and De Moivre, were applying themselves at the same time to similar pursuits. Several members of the Academy of Sciences at Paris, were the authors of various useful investigations relating to practical mechanics; but not many of these were given to the public till after the year 1700; some of their inventions made their appearance much later, in the "Collection of Machines," approved by the Academy; and some of them have been inserted in a work published at Leipsic, under the title of "Theatrum Machinarum." Throughout the whole of the last century, the Transactions of various societies, established for the promotion of science, became every year more numerous; and the publication of literary and philosophical journals at Leipsic and Paris, formed a mode of communication which was extremely serviceable in facilitating the dissemination of all new discoveries. In our own country, we have had, during the last century, a great number of instances, in which practical invention, and the most comprehensive science, have been united; and |