MACHINE ; MACHINERY. The advan tage which any machine affords for overcoming resistance consists in the reaction by which it supports a certain portion of the weight pro ducing that resistance, so that the motive power has only to counteract the remainder. This may be immediately observed in those simple machines called the mechanical powers. For example, in the lever, the wheel and axle, and the pulley, any convenient portion of the resistance may be made to rest on the point of support, or the point of suspension. Again, in the inclined plane, the wedge, and the screw, the motive power, the resistance and the reaction of the support, being, in the case of equilibrium, represented by the three sides of a triangle, the ratio of the first to either of the others may be varied at pleasure by the construction of the machine.
The powers employed to give motion, through machinery, to any object, are produced by the muscular strength of men or animals ; the actions of weights, springs, wind, water, steam, or fired gunpowder ; and these powers may generally be considered as pressures exerted during certain portions of time. Even that power which is produced by a sudden impulse, as when a rammer descending by its weight falls on the head of a pile, is only a pressure existing during an indefinitely short interval of time. The point in any machine
to which the moving power is applied is called the impelled point, and that against which the resistance acts is called the working point.
In the classification proposed by Dr. Lyon Play fair, and adopted by the Commissioners at the Great Industrial Exhibition, machinery forms one of the four great divisions into which the specimens exhibited are to be dis posed ; and this division is subdivided into six classes ; viz. 1. Machines for direct use, including carriages, and railway and naval mechanism ; 2. Manufacturing machines and tools ; 3. Mechanical, civil engineering, archi tectural and building contrivances ; 4. Naval architecture, military engineering and struc ture, ordnance, armour, and accoutrements ; 5. Agricultural and horticultural machines and implements ; 6. Philosophical, musical, horological, acoustical, and miscellaneous in struments. This classification is doubtless convenient for the immediate object in view ; but it gives to the word machinery' a much wider application than is ordinarily adopted.
Our exports of machinery and mill-work in 1850 amounted in value to 1,043,764/.