This change has been due in great
measure to the introduction of very economical marine engines, chiefly
of the compound type, together with better boilers carrying a higher
pressure.
The speed and regularity of ocean steamers has also greatly improved,
and one small scientific improvement has added much to the safety of
traversing such seas as the Atlantic at a high speed--namely, the
careful and continual use of a good thermometer, to ascertain constantly
the temperature of the sea-water at the surface. For if an iceberg is
floating within a quarter of a mile--or even half a mile, if the sea is
pretty smooth--the surface water will be several degrees colder than the
rest of the sea; since the very cold fresh water, resulting from the
melting iceberg, floats on the top of the sea water for some distance.
No doubt the use of iron, and now of steel, has contributed most largely
to the increase of shipbuilding in this country. Good arrangements
of water ballast have also proved very useful; and steam cranes and
arrangements for loading and discharging cargo have greatly promoted the
use of steam colliers, enabling them to make more voyages in the year.
Closely connected with marine engineering is the great improvement in
the economy of stationary engines, which has become more fully developed
during recent years, both in reference to waterworks engines and factory
engines.
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