The position of the reversing link is altered by means of a cord, passing over two pulleys, fixed respectively in the engine-house and on the derrick.
The substitution of machinery for hand labour in cutting coal has long been a favourite problem with inventors, the earliest plan being that of Michael Meinzies, in 1761, who proposed to work a heavy pick underground by power transmitted from an engine at the surface, through the agencies of spear-rods and chains passing over pulleys; but none of the methods suggested proved to be practically successful until the general introduction of compressed air into mines furnished a convenient motive power, susceptible of being carried to considerable distances without any great loss of pressure.
The surface arrangements of a modern deep colliery are of considerable extent and complexity, the central feature being the head gear or pit frame carrying the guide pulleys Surface which lead the winding roes from the axis of the it arrange= g P P to the drum.
8) the guide pulleys G1, G2 are carried upon an arm free to turn about the axis 0.
The other six are connected to each other and to the lowest one by wire cables and pulleys in such a way that when the cable which connects the two lowest tubes is wound in by means of a winch, each of the tubes except the fixed one will rise within the next one through the same distance.
(The architect being at that time also the contractor.) The chapters are -- (1) on various machines, such as scaling-ladders, windmills, &c.; (2) on windlasses, axles, pulleys and cranes for moving heavy weights, such as those used by Chersiphron in building the great temple of Diana at Ephesus, and on the discovery by a shepherd of a quarry of marble required to build the same temple; (3) on dynamics; (4) on machines for drawing water; (5) on wheels for irrigation worked by a river; (6) on raising water by a revolving spiral tube; (7) on the machine of Ctesibius for raising water to a height; (8) on a very complicated water engine, the description of which is not intelligible, though Vitruvius remarks that he has tried to make the matter clear; (9) on machines with wheels to register the distance travelled, either by land or water; (10) on the construction of scorpiones for hurling stones; (11) and (12) on balistae and catapults; (13) on battering rams and other machines for the attack of a fortress; (14) on shields (testudines) to enable soldiers to fill up the enemy's ditches; (15) on other kinds of testudines; (16) on machines for defence, and examples of their use in ancient times.
But a floor, however heavy, suspended by three wire ropes and properly balanced over large, well-mounted pulleys, requires an amount of energy to work it which does not exceed that required to operate a platform of moderate dimensions, and there is a freedom, a safety and a facility of working with a complete floor which no partial platform can give.
The Torque Was Measured By Weights 0 And P Suspended By Silk Ribbons Passing Over The Pulleys N And Round The Disk Kl.
Suppose the base-circles to be a pair of circular pulleys connected D~ ill by means of a cord whose course ~f from pulley to pulley is P1IP2.
As the line of connection of those pulleys is the same as that of the I proposed teeth, they will rotate -
Wrapping ConnectorsBelts, Cords and Chains Flat belts of leather or of gutta percha, round cords of catgut, hemp or other material, and metal chains are used as wrapping connectors to transmit rotatory motion between pairs of pulleys and drums.
A belt tends to move towards that part of a pulley whose radius is greatest; pulleys for belts, therefore, are slightly swelled in the middle, in order that the belt may remain on the pulley, unless forcibly shifted.
Chains require pulleys or drums, grooved, notched and toothed, so as to fit the links of the chain.
Wrapping connectors for communicating reciprocating motion have usually their ends made fast to the pulleys or drums which they connect, and which in this case may be sectors.
Pulleys and drums for communi cating a constant velocity ratio are circular.
The angular velocities of a pair of connected circular pulleys or drums are inversely as the effective radii.
The length L of an endless belt connecting a pair of pulleys whose effective radii are r,, r,, with parallel axes whose distance apart is c, is given by the following formulae, in each of which the first term, containing the radical, expresses the length of the straight parts of the belt, and the remainder of the formula the length of the curved parts.
When the a,ces of a pair of pulleys are not parallel, the pulleys should be so placed that the part of the belt which is approaching each pulley shall be in the plane of the pulley.
The speed-cones are either continuous cones or conoids, as A, B, whose velocity ratio can be varied gradually while they are in motion by shifting the belt, or sets of pulleys whose radii vary by steps, as C, D, in which case the velocity ratio can be changed by shifting the belt from one pair of pulleys to another.
One train of mechanism may diverge into two or moreas when a single shaft, driven by a prime mover, carries several pulleys, each of which drives a different machine.
F = T1 Ti = T1 (I ef9) Ta(ef 1)j When a belt connecting a pair of pulleys has the tensions of its two sides originally equal, the pulleys being at rest, and when the pulleys are next set in motion, so that one of them drives the other by means of the belt, it is found that the advancing side of the belt is exactly as much tightened as the returning side is slackened, so that the mean tension remains unchanged.
Trans., 1894) investigated the question for the cases of loaded and unloaded shafts, and, owing to the complication arising from the application of the general theory to the cases of loaded shafts, devised empirical formulae for the critical speeds of shafts loaded with heavy pulleys, based generally upon the following assumption, which is stated for the case of a shaft carrying one pulley: If Ni, N1 be the separate speeds of whirl of the shaft and pulley on the assumption that the effect of one is neglected when that of the other is under consideration, then the resulting speed of whirl due to both causes combined may be taken to be of the form N1N2~!
This form is extended to include the cases of several pulleys on the same sifaft.
Such persons may sometimes get a good deal of exercise in a short time by the use of dumb-bells, of elastic cords, or of cords running over pulleys and weighted at one end.
These wheels receive motions from bands and pulleys from a steam or other engine contained in the car.
Wheels creak on their axles as the cogs engage one another and the revolving pulleys whirr with the rapidity of their movement, but a neighboring wheel is as quiet and motionless as though it were prepared to remain so for a hundred years; but the moment comes when the lever catches it and obeying the impulse that wheel begins to creak and joins in the common motion the result and aim of which are beyond its ken.
Just as in a clock, the result of the complicated motion of innumerable wheels and pulleys is merely a slow and regular movement of the hands which show the time, so the result of all the complicated human activities of 160,000 Russians and French--all their passions, desires, remorse, humiliations, sufferings, outbursts of pride, fear, and enthusiasm--was only the loss of the battle of Austerlitz, the so-called battle of the three Emperors--that is to say, a slow movement of the hand on the dial of human history.