be used for the purpose of building vessels. With respect to marine
engines, they are now supplied with steam from multiple tubed boilers,
the shells of which are commonly cylindrical. They are of enormous
strength, and made with every possible care, and carry from 80 lb. to
100 lb. pressure on the square inch.

It has been found, on the whole, more convenient to expand the steam
in two or more cylinders, rather than in one. I quite agree that, as a
mere matter of engineering science, there is no reason why the
expansion should not take place in a single cylinder, unless it be
that a single cylinder is cooled down to an extent which cannot be
overcome by jacketing, and which, therefore, destroys a portion of the
steam on its entering into the cylinder.

As regards the propeller, as we know, except in certain cases, the
paddle-wheel has practically disappeared, and the screw propeller is
all but universally employed. The substitution of the screw propeller
for the paddle enables the engine to work at a much higher number of
revolutions per minute, and thus a very great piston speed, some 600
ft. to 800 ft. per minute, is attained; and this, coupled with the
fairly high mean pressure which prevails, enables a large power to be
got from a comparatively small-sized engine. Speeds of 15 knots an
hour are now in many cases maintained, and on trial trips are not
uncommonly exceeded. Steam vessels are now the accepted vessels of
war. We have them in an armored state and in an unarmored state, but
when unarmored rendered so formidable, by the command which their
speed gives them of choosing their distance, as to make them, when
furnished with powerful guns, dangerous opponents even to the best
armored vessels.

MARINE GOVERNORS.

We have also now marine engines, governed by governors of such extreme
sensitiveness as to give them the semblance of being endowed with the
spirit of prophecy, as they appear rather to be regulating the engine
for that which is about to take place than for that which is taking
place. This may sound a somewhat extravagant statement, but it is so
nearly the truth, that I have hardly gone outside of it in using the
words I have employed. For a marine governor to be of any use, it must
not wait till the stern of the vessel is out of the water before it
acts to check the engine and reduce the speed. Nothing but the most
sensitive, and, indeed, anticipatory action of the governors can
efficiently co