STATICS, a term which the modern improvements in knowledge have made it xecessary to introduce into physico-ma thematical science. It was found conveni ent to distribute the doctrines of univer sal mechanics into two classes, which re quired both a different mode of considera tion, and different principles of reasoning. We are indebted to Archimedes for the Ihndamental principles of this science. He investigated the doctrine of the centre of gravity, and the theory of the lever. But the subject of moving forces was not pro perly understood, till Galileo considered it very accurately in his work on " Local Motion." In this, he considers a change of motion as the exact and adequate mea sure of a moving force ; and he considers every kind of pressure as competent to the production of such changes. He applied this principle to the motion of bodies by the action of gravity, and gave the theory of projectiles. Sir Isaac Newton took up the subject nearly as Galileo had left it, and applied the doctrines, which had been previously called in aid of mechanics only, to explain the celestial motions ; and the magnificence of this subject caused it to occupy the whole attention of mathema ticians. The " Principia" contained, in deed, propositions equally conducive to the improvement of common mechanics, and to the complete understanding tithe mechanical actions of bodies. Philoso phers began to make their applications. They saw that every kind of work that is performed by a machine may be consider ed abstractedly as a retarding force ; that the impulse of water or wind, which are employed as moving powers, act by means of pressures which they exert on the im pelled point of the machine; and that the machine itself may be considered as an as semblage of bodies, moveable in certain limited circumstances, with determined directions and proportions of velocity. From these Considerations resulted a ge neral abstract condition of a body acted upon by known powers: at length was de termined a new kind of equilibrium, not thought of by ancient mechanicians, be tween the resistance to the machine per forming work and the moving power, which exactly balance each other ; and is indicated, not by the rest, buI by the uni form motion of the machine. Ilence also the mathematician was enabled to calcu late the precise motion of water which would completely absorb, or balance the superiority of pressure by -which water is forced through a sluice, pipe, &c. with a constant velocity.
Thus the general doctrines of motion came to be considered in two points of view, according as they balanced each other in a state of rest, or of uniform mo tion. These two ways of considering the same subject required both different prin ciples and a different manner of reasoning. The first has been named statics, as ex pressing that rest which is the test of this kind of equilibrium. The second has been called dynamics, or universal mechanics, because the different kinds of motion are characteristic of the powers or forces which produce them. A knowledge of both is indispensably necessary for ac quiring any useful practical knowledge of machines: and it was ignorance of the doctrines of accelerated and retarded mo tions, which made the progress of practical mechanical knowledge so very slow and imperfect. The mechanics, even of the moderns, before Galileo, went no further than to state the proportion of the power and resistance which would be balanced by the intervention of a given machine, or the proportion of the parts of a ma chine, by which two known forces may balance each other. This view of the mat
ter introduced a principle, which even Galileo considered as a mechanical axiom, viz. that what is gained in force, by means of a machine, is exactly compensated by the additional time which it obliges us to employ. This is not quite accurate, and not only prevents improvement in the construction of machines, but leads to er roneous maxims of construction. The two principles of dynamics teach us, that there is a certain proportion of the machine de pendent on the kind and proportion of the power and resistance, which enables the machine to perform the greatest possible work. It is highly proper, therefore, to keep separate these two ways of donsid ering machines, that both may be improv ed to the utmost, and then to blend them together in every practical discussion. Statics, therefore, is preparatory to the proper study of mechanics ; but it does not hence derive all its importance. It is the sole foundation of many useful parts of knowledge. This will be best seen by a brief enumeration. 1. It comprehends all the doctrines of the excitement and propagation of pressure, through the parts of solid bodies, by which the energies of machines are produced. A pressure is ex erted on the impelled point of a machine,' such as the float-boards or buckets of a mill-wheel. This excites a pressure at the pivots of its axle, which act on the points of support. This must be under stood, both as to direction and intensity, that it may be effectually resisted. A pressure is also excited at the acting tooth of the cog-wheel, on the same axle by which it urges round another wheel, exerting similar pressures its pivots, and on the acting tooth perhaps of a third wheel. Thus a pressure is ultimately ex cited in the working point of the machine, perhaps a wiper,which lifts a heavy stamp er, to let it fall again on some matter to be pounded. Now statics teaches us the intensities and direction of all those pres sures, and therefore how much remains at the working point of the machine un balanced by resistance. 2 It comprehends every circumstance which influences the stability of heavy bodies; the investigation and properties of the centre of gravity ; the theory, of the construction of arches, vaults and domes ; the attitudes of animals. 3. The strength of materials, and the prin ciples of construction, so as to make the proper adjustment of strength and strain, in every part of a machine, edifice, or structure of any kind. Statics, therefore, furnishes us with what may be called a theory of carpentry, and gives us proper instructions for framing floors, roofs, cen tres, &c. 4. Statics comprehends the whole doctrine of the pressure of fluids, whether liquid or ariform, whether aris ing from their weight, or from any ex ternal action. Hence, therefore, we de rive our knowledge of the stability of ships, or their power of maintaining them selves in a position nearly upright, in op position to the action of the wind on their sails. We learn on what circumstances of figure and stowage this quality depends, and what will augment or diminish it.
See DYNAMICS, MECHANICS, &c. •