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.

The great steamer went ahead at the rate of five nautical miles an
hour, and the cable passed smoothly overboard. Messages were sent to
England and answers received. The weather was bright, and all hands
were cheerful. On the third day after the "splicing" of the shore-end
with the main cable, that part of the ocean was reached where the water
suddenly increases in depth from two hundred and ten fathoms to two
thousand and fifty. One of the earlier cables broke at this place and
was lost forever. The electricians and engineers watched for it with
anxious eyes. It was reached and passed. The black cord still traveled
through the wheels unbroken, and the test applied by the galvanometer