Fig. 36 is an intermittent motion given the is constant, as in the case of dock devices, tilt times of vibration are equal; (2) that when the force of gravity is constant, as is the case of any given point on the surface of the earth, the time of vibration varies directly as the square root of the length of the pendulum, so that, if a pendulum of a given length vibrates in one second, a pendulum one-quarter as long will vibrate in one-half of a second, and one font times as long will vibrate in two seconds; (31 that when the length of the pendulum is con stant, the time of a vibration varies inverse]; as the square root of the force of gravity; and (4) that when the time of vibration of two toothed wheel by the rotation of the notched pinion. Every time the notch comes around it advances the wheel one tooth.
Fig. 37 is an escapement. The levers arc connected with a pendulum or the like and at every swing allow the wheel to turn one notch.
Fig. 38 is a ball governor as used on steam engines. When a certain speed is exceeded the balls are thrown out by centrifugal force, and rise, opening a valve or adjusting a cut-off and thus reducing the speed back to the normal.
°Compound motions" are obtained by com bining any two or more of the simple motions, and machines are built up by combining the simple motions harmoniously.
pendulums at aifferent points on the surface of the earth is equal, their lengths vary directh as the force of gravity. Sec PENDULUM.
"Perpetual motion" is a continuous or inces sant motion supposed to be attainable by a me chanical device with inherent motive and, therefore, which when once set in motion capable of continuing that motion indefinitely o: perpetually. Such a device or machine, if prac ticable, might be termed a ((perpetual move. meat." The various forms of mechanical movement> embodying the principles of one or more of the mechanical powers already described are SO in numerable that a detailed description of titer °Pendulum motion" is the oscillatory motion of a body in the arc of a circle, the body being attached to a rod which vibrates to and fro from a fixed axis. In the ideal simple pen dulum, consisting of a body attached to a string without weight and vibrating from the point of suspension without resistance of any kind whatever, a material body once set in motion would continue to swing to and fro forever.
Under these conditions it has been noted (1) that the time of vibrations of a pendulum through short arcs is independent of the lengths of the arcs and that when the length of the arc is impracticable within the scope of this artielci hut they are classified as follows into seven important groups according to the general Pul poses for which they are used.
"Transmission of power appliances,* consist ing of ropes, belts and various forms of gum pulleys, etc.
of power appliances and used for determining velocities, pres sures, weights, number and quantities, such a; brakes, counters, dynamometers, gauges, indica tors, meters, planimeters, testing machines are weighting machines.
"Steam power appliances,* comprising boil ers, locomotives, locomotive engines, oscillating engines, rotary engines, steam-engines, steam turbines, valves and valve-gears, parallel motion gears, governors and other engine devices.
"Steam appliances," such as injectors, steam pumps, condensers, separators, traps and valves.
"Motive power machines," such as gas-en gines, internal-combustion engines, heat-en gines, solar engines, etc.
"Hydraulic power appliances and devices,* consisting of various forms of waterwheels, water-motors, turbines, pumps, syphons, water lifts, ejectors, hydraulic or water rams, meters, indicators, pressure regulators, valves, pipe joints, filters, hydraulic presses and hydraulic stop motions, wipers, shafts, couplings and gyro scopes.
"Hornlogical apparatus and devices," mainly used for measuring time, such as spring and pendulum clocks, watch and chronometer move ments, electric clocks and sundials.
"Mining machinery and appliances? such as quarrying and cutting machines, borers, drills, valves, blowers, ventilators, safety lamps, hoist ing drums, conveyors, crushers, pulverizers, hy draulic nozzles, presses, air-blast and magnetic separators, steam shovels, dredges, haulage ap pliances, furnaces and automatic dumps.
"Mill and factory appliances," such as hang ers, shaft bearings, ball bearings, steps, coup lings, universal and flexible couplings, speed metal-working machinery such as riveters, rail benders and punches.
"Air power appliances," devices and tus consisting of air compressors, air pumps, air water-lifts, barometers, bellows, blowers, blow pipes and compressed-air tools such as pneu matic drills, hammers, riveters and shearing ma chines. Also, gauges, ventilators and musical instruments.