Scientific American Supplement, No. 312, December 24, 1881 | Page 6

for warlike purposes. As in the case of the
wagon boilers, the boilers of the paddle steamers of 1831 were most
unsuited for resisting pressure. They were mere tanks, and there was as
much pressure when there was no steam in the boiler from the weight
of the water on the bottom, as there was at the top of the boiler from the
steam pressure when the steam was up. Under these circumstances,
again, from 3½ lb. to 5 lb. was all the pressure the boilers were
competent to bear, and as the engines ran at a slow speed, they
developed but a small amount of horse-power in relation to their size.
Moreover, as in the land engine, the connection between the parts of
the marine engine was such as to be incompetent to stand the strain that
would come upon it if a higher pressure, with a considerable expansion,
were used, and thus the consumption of coal was very heavy; and we
know that, having regard to the then consumption, it was said, on high
authority, it would be impossible for a steamboat to traverse the
Atlantic, as it could not carry fuel enough to take it across; and indeed
it was not until 1838 that the Sirius and the Great Western did make the
passage. The passage had been made before, but it was not until 1838
that the passenger service can be said to have commenced. In 1831, the
marine boiler was supplied with salt water, the hulls were invariably of
wood, and the speed was probably from eight to nine knots an hour. In
1881, the vessels are as invariably either of iron or of steel, and I
believe it will not be very long before the iron disappears, giving place
entirely to the last mentioned metal. With respect to the term "steel," I
am ready to agree that it is impossible to say where, chemically
speaking, iron ends and steel begins. But (leaving out malleable cast
iron) I apply this term "steel" to any malleable ductile metal of which
iron forms 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 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