been
viewed in this connection, however, merely as a curiosity, and led to no
immediate results. Later, in 1804, Francis B. Stevens, of New Jersey, in
an experimental boat on the Hudson, operated twin screws, and
demonstrated their applicability to the requirements of marine practice.
These propellers, in fact, had a form far more nearly approaching the
modern screw-propeller than did those which came somewhat later, and
which marked the real entry of the screw-propeller into actual and
practical service.

Again, in 1812, Ressel, a student in the University of Vienna, began to
study the screw-propeller, and his first drawing dates from this time.
In 1826 he carried on experiments in a barge driven by hand, and in 1827
an Austrian patent was granted him. Two years later he applied his screw
to a boat with an engine of six horse-power, and a speed of six miles
per hour was said to have been attained. Then came a bursting
steam-pipe, and the police put a stop to the experiments, which seem to
have had no further results.

Likewise in 1823 Captain Delisle, of the French Engineers, presented a
memorial to his Government in which he urged the use of the submerged
propeller for the propulsion of steam vessels. No especial attention was
given to the suggestion, however, and it was apparently forgotten until
later, when the propeller had become a demonstrated success. Then this
memorial was remembered, and its author brought forward to receive his
share of credit in connection with the adaptation of the propeller to
marine propulsion.

These various attempts to introduce the screw-propeller seem curiously
enough to have had no lasting result. They were not followed up, and in
the mean time had to some extent passed out of memory, or, if
remembered, the absence of result can hardly have acted as an incentive
to fresh effort. At the same time it must be admitted that the
screw-propeller as a possibility for marine propulsion was known in a
vague way to the engineering practice of the day, and it is at this time
of course quite impossible to say how much may have been known by
Ericsson, Smith, or others concerned in later developments, or to what
extent they may have been dependent for suggestion on what had preceded
them. The question of who invented the screw-propeller in the absolute
sense is entirely futile and without answer. No one could ever have
reasonably advanced any such unique claim. At the best it is simply a
ques