tion of the relative influence in the introduction, improvement, and
practical application of what was the common property of the engineering
practice of the day.

In 1833, or at the period now under consideration, however, the
paddle-wheel was the recognized instrument of marine propulsion. Since
the beginning of the century it had been growing in use with the gradual
growth in the application of steam, and at this time it held the field
alone. Some years earlier it appears that some of the objections to the
paddle-wheel had become plainly apparent to Ericsson, although,
occupied with other matters as he was, there was no immediate result. He
apparently recognized that the slow revolutions possible with the
paddle-wheel did not favor the improvement of the steam-engine along the
lines which have since been followed, and he saw clearly that for
warship purposes the engines employed, exposed above the water-line to
destruction from the shell of an enemy, were entirely out of the
question. Finally in 1833 and 1834 we find him employed by a carrying
company in London to conduct numerous trials with submerged propellers
in the London and Birmingham canal. In an affidavit made in March, 1845,
he states that in 1833 his attention was particularly called to the
subject of oblique propulsion, and that under his direction propellers
of various patterns and embodying these principles were fitted on a
canal-boat named the "Francis," and later in 1834 to another called the
"Annatorius." Shortly after this, or in 1835, his ideas took more
definite form, and he refers to his work in a letter to his friend John
Bourne in the following terms:--

"1835. Designed a rotary propeller to be actuated by steam-power
consisting of a series of segments of a screw attached to a thin broad
hoop supported by arms so twisted as also to form part of a screw. The
propeller subsequently applied to the steamship 'Princeton' was
identical with my said design of 1835. Even the mode adopted to
determine, by geometrical construction, the twist of the blades and arms
of the 'Princeton's' and other propellers was identical with my design
of the year last mentioned."

At about this same time, or in 1835, the attention of Mr. F.P. Smith
seems to have been drawn to the subject of the screw-propeller, and we
find him taking out a patent for his form, consisting of an elongated
helix or spiral of several turns, under date of May 31, 1836. Ericsson's
patent fol