a greater percentage of the power of the steam is utilized and
four or five times the work obtained from coal over that of the
old system. The side-wheel was continued in use in the older
ships until this period, but after 1870 it disappeared.

It has been said that the life of iron ships, barring disasters
at sea, is unlimited, that they cannot wear out. This
statement has not been tested, but the fact remains that the
older passenger ships have gone out of service and that steel
has now taken the place of iron, as lighter and more durable.

Something should also be said here of the steam turbine
engine, recently introduced in some of the greatest liners, and of
proven value in several particulars, an important one of these
being the doing away with the vibration, an inseparable
accompaniment of the old style engines. The Olympic and
Titanic engines were a combination of the turbine and reciprocating
types. In regard to the driving power, one of the recent
introductions is that of the multiple propeller. The twin
screw was first applied in the City of New York, of the Inman
line, and enabled her to make in 1890 an average speed of a
little over six days from New York to Queenstown. The best
record up to October, 1891, was that of the Teutonic,
of five days, sixteen hours, and thirty minutes. Triple-screw
propellers have since then been introduced in some of the
greater ships, and the record speed has been cut down to the
four days and ten hours of the Lusitania in 1908 and the
four days, six hours and forty-one minutes of the Mauretania
in 1910.