eriment of building two vessels of the same
size and power, the one with paddles the other with a screw, and finding
the screw still superior, it was finally adopted as an auxiliary to the
sails. Little thought the naval experts of that period, that another
fifty years or so would see both sails and wooden ships quite obsolete--
as far as the Navy was concerned at any rate.

These experiments showed clearly that the screw was absolutely essential
to every warship, as in a calm, the finest sailing ship would be at the
mercy of any small steamer, armed with long-range guns. Thus while new
vessels were laid down specially designed to carry screws, wherever it
was found possible to do so, all the efficient battleships and frigates
were fitted with auxiliary engines. Of course these converted sailing
ships, not having been designed for the purpose, could only carry
engines of small power, still, it was a case of half a loaf being better
than no bread, and was the best that could be done under the
circumstances.

The first propellers were in the form of an ordinary screw thread, but
it was soon found that separate fans were equally satisfactory, and more
convenient to make. Much discomfort was caused by the excessive
vibration caused by the early screws, but various improvements in their
design reduced this. The fans of the screws are now attached by means
of; bolts to a hollow sphere on the end of the shaft, and should a fan
be damaged, it can be readily replaced. At first all screws were so
constructed, that they could be lifted up through a well when sails
alone were being used, so that it would not impede the ship. The
funnels, too, being made to shut up like a telescope, a steamer could
thus be easily turned into a sailing ship.

At the very time that the screw propeller was initiating a revolution in
the method of steam propulsion, another revolution was taking place in
shipbuilding material. Iron barges had been used as far back as 1787,
and an iron steamer had been built at Tipton about the year 1821, but
for another twenty years iron ships were not viewed with favour, and
only began to force their way to the front about the beginning of the
reign of Queen Victoria. Even then they were deemed utterly unsuitable
for war vessels, as being very difficult to repair and keep afloat when
perforated by the enemy's shot, as they must inevitably be in action.
But in the course of time, the iron vessel naturally rais