It may seem a simple matter to distribute or "pay out" the cable, but in practice it is exceedingly difficult. Twenty men are stationed in the tank from which it is issuing, each dressed in a canvas suit, without pockets, and in boots without nails. Their duty is to ease each coil as it passes out of the tank, and to give notice of the marks painted on the cable one mile apart. Near the entrance of the tank it runs over a grooved wheel and along an iron trough until it reaches that part of the deck where the "paying out" machine is placed. The latter consists of six grooved wheels, each provided with a smaller wheel, called a "jockey," placed against the upper side of the groove so as to press against the cable as it goes through, and retard or help its progress. These six wheels and their jockeys are themselves controlled by brakes, and after it has been embraced by them the cable winds round a "drum" four times. The drum is another wheel, four feet in diameter and nine inches deep, which is also controlled by powerful brakes; and from it the cable passes over another grooved wheel before it gets to the "dynamometer" wheel. The dynamometer is an instrument which shows the exact degree of the strain on the cable, and the wheel attached to it rises and falls as the strain is greater or less. Thence the cable is sent over another deeply grooved wheel into the sea. You will remember what I said about insulation,--how a tiny hole in the gutta-percha would allow the electricity to escape. On deck there is a small house, which is filled with delicate scientific instruments. As the cable is paid out, it is tested here. If a wire or a nail or a smaller thing is driven through it, and the insulation is spoiled, an instrument called the galvanometer instantly records the fact, and warning is given at all parts of the ship. The man in charge touches a small handle, and an electric bell rings violently in the tank and at the paying-out machinery. At the same time a loud gong is struck, at the sound of which the engines are stopped. Delay might cause much trouble or total failure, as the injured section must be arrested and repaired before it enters the water.