the principal element and which has been in fusion, and I do so in
contradistinction to the metal which may be similar chemically, but
which has been prepared by the puddling process. Applying the term
steel in that sense, I believe, as I have said, it will not be very
long before plate-iron produced by the puddling process will cease to
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