ithout status or recognition as a
commercial or practical means for propelling ships. So far as the
screw-propeller was thought of as a means of propulsion, it lay under a
suspicion of loss of efficiency due to the oblique nature of its action,
and this was supposed to be such as to render it necessarily and
essentially less efficient than the paddle-wheel.

Ericsson lived to see the use of sails almost entirely discarded for war
purposes, and for mercantile purposes relegated to ships for special
service and of continually decreasing importance. He lived to see the
steam-engine take its place as the only means for supplying the power
required to propel warships, and attain a position of almost equal
relative importance in the mercantile marine. He lived to see the
paddle-wheel grow in importance and estimation as a means of propulsion
only in turn to be supplanted by the screw-propeller, which gradually
increased in engineering favor from the days of its obscure infancy
until it became the only means employed for the propulsion of ships
navigating the high seas, while it had become a most serious rival to
the paddle-wheel even for the purposes of interior and shallow-water
navigation,--long a field considered as peculiarly suited to the
paddle-wheel and to the engines adapted to its operation.

Regarding the change from wind to steam for the motive-power of ships,
Ericsson did his full share among the engineers of his day, but it would
be unfair to many others to claim for him any exclusive or
preponderating influence in this movement, and in such matters it is
difficult to clearly define the services of any one man. The lines of
progress, however, have been in accord with his studies, and his work
has certainly had a most direct and powerful influence upon the
movement. The most important points of contact between Ericsson's work
and these advances were in connection with his introduction of the
surface condenser, the use of artificial draft, devices for heating feed
water, his studies in superheated steam and its use, and his work in
connection with the development of the compound principle in
steam-engines, his relation to the introduction of the screw-propeller,
and to the use of twin screws at a later time. He also devised and
adapted many new types of engines for marine purposes, having respect to
the geometrical character of the connections by means of which a
reciprocating motion of the piston may be transform