APPLIANCES FOR TIIE TRANSMISSION Or POWER.
A complete machine or set of machines is made up of three parts: (1) the prime mover or motor, which receives its motion and force from a natural source, as from animals, water, wind, or steam; (2) transmitting appliances, such as ropes, chains, belts, levers, wheels, tooth-gearing, shaft ing, or their combinations; and (3) the machine proper which receives the transmitted power. Motors and machines having been fully treated in the preceding pages, the appliances for the transmission of motion and force will alone be considered in this section. We may first observe that the force acting and the object acted upon are separate and distinct, and that while the object of motive force is to drive a machine, the motor can operate it only through connecting arms. These arms (ropes, connecting rods, mechanical movements, etc.) are properly transmitting machines, the form and strength of whose mechanism depend on the amount and direction of the motion, and on the force to be conveyed.
Rope the various expedients devised by man for the purpose of assisting in his work, the simple process of pulling would nat urally first be suggested as a means of moving an object. In fact, this process, through the medium of a rope, was one of the earliest methods employed—as, for example, traces, by which animals were attached to sledges and wagons. (See p. 309.) In similar methods of attachment Nature antedates all human inventions, as is shown by the tendons and ligaments, which are a direct means of connection between the motor muscles and the parts of the body to be moved, and which, taken as a whole, effect in an admirable manner all the animal movements, pre senting at once the most convincing proof of original and perfected mechanical contrivance for directing and utilizing muscular force.
An ancient means for reaching and drawing distant objects by the direct application of hand-power is shown in Figure 1 (pl. 119), which represents the Eastern method of raising water from wells with rope and vessel. Paconius, according to Vitrnvius, in order to transport from the quarry a new base for a colossal statue of Apollo in the temple, constructed a machine (fig. 2) consisting of two framed-up wheels (A, A, the diameter of
each being about 15 feet), in which he inserted the ends (C) of the stone, which was 12 feet long, 8 feet wide, and 6 feet high. From wheel to wheel in their circumferences around the stone were fixed 2-inch spindles (D) about 12 inches apart. Around the spindles was wound a rope, to one end of which were attached oxen which, by drawing on the rope and unwinding it, caused the machine to revolve along the surface of the ground; in this manner, by repeated adjustment of the rope, the stone was transported to the site of erection.
and works describe and illustrate various examples of rope-and-pulley transmission employed in raising water and in moving heavy bodies by men and draught animals. (See pis. 61, 112.) If we include modern pulley-blocks (tackles) and hand and power-lifts (pl. io8), the varieties will be found to be very numerous.
In Italy in the sixteenth century there was employed a simple but ingenious method of rope transmission by which persons in the upper stories of a building could readily elevate water from a well or cistern at some distance. Figure 3 (p/. 119) exhibits this contrivance, which consists of a cord tightly stretched from the ground to a beam projecting from the story to which the water is to be raised. Upon this cord there is a bulb or collar located centrally over the well and as a stop. The bucket-rope passes through a ring which slips freely upon the stretched cord, and thence over a fixed pulley in the end of the beam to the hands of the operator. As the bucket and ring glide down the cord, the ring is arrested by the bulb on the stretched cord, but the bucket is lowered to the water in the well. When the bucket is filled it is with drawn by pulling on the bucket-rope, on which is a knot that comes in contact with the ring, which then slides up the cord and guides the bucket to the hands of the person operating the rope.