LEVIATHAN

Therefore in this, as in all mechanical engines, when a small power raises a great weight the velocity of the power is much greater than the velocity of the weight; and what is gained in force is therefore said to be lost in time. When the power and the weight do not act on the lever in directions perpendicular to its lengtli, or when the arms of the lever are not in the same straight line, or are bent, then the power and the weight are not to each other reciprocally as the arms of the lever, but as the straight lines drawn from the fulcrum perpendicular to the respective directions in which the power and the weight take effect. Examples of the application of the lever are of constant occurrence in the mechanical arts. The crowbar, the handspike, the poker, sci ars, nippers, pincers, ., are levers of the first kind; the toothed hammer is only a bent lever of this kind. The second kind includes the chipping knife, nutcrackers, the common door, oars and rudders, the wheelbarrow, . To levers of the third kind belong the sheep-shears, the treddle of the turning lathe, tongs, .: these have a mechanical disadvantage, but admit of a proportionally wider motion. The bones of animals are generally levers of this sort. The socket of the bone is the fulcrum; a strong muscle attached to it near the socket is the power; and the weight of the limb, with whatever resistance is opposed to its motion, is the weight. A very moderate contraction of the muscle thus gives considerable motion to the limb. From the principle of the lever is deduced the distribution of pre ure in the case of a pole bearing an intermediate weight. If the weight hang from the middle, the carriers will share the burden alike; but if a load is laid over the pole, and a vertical from its centre of gravity divides the length unequally, as will be the case on altering the inclination of the pole (for example, in climbing a hill), then the bearer nearest to whom the vertical falls suffers a greater strain than the other. Universal Lever is the name given to a machine formed of a combination of the lever with the wheel and axle, the object of which is to give a continued rectilinear motion to a heavy body by means of the reciprocating motion of the lever. F G H is a straight line, whose centre of motion is at G. At the extremity of its shorter arm hang two bars, the former of which has a hook to catch into the teeth of the wheel A C D, while the latter has its end bent in order to slide over the outer parts of those teeth. The axle A has a cord wound round it, to the end of which is attached the weight W. Now suppose the end H of the lever to be raised from H to I, while the other end descends from F to B; the bar F E will then push the tooth E of the wheel to C, while the hook D slides over an equal space on the other side of the wheel. On bringing down again the end of the lever from I to H, the other extremity ascends through B F, and the hook D raises up the left-hand side of the wheel through a space equal to E C. Thus the reciprocating motion of the lever is made to communicate a continued rotatory motion to the wheel, and, consequently, to lift the weight W suspended from its axle bv the cord. The universal lever has long been employed in saw-mills, for the purpose of drawing along the logs to the saw. {Gregory's Mechanics, vol. ii.) LE V [s. 671]