n termed, and later with caloric engines in
smaller sizes for stationary purposes, of which several thousand were
sold during the next succeeding years.

In the work of introducing his propellers good progress was made,
especially in boats built for use on the Great Lakes, so that by 1844,
when the U.S.S. "Princeton" went into commission, there were in use some
twenty-five vessels with the screw-propeller as a means of propulsion.

The project of building a vessel for the American Navy, the purpose
which had most strongly attracted Ericsson to the United States,
suffered long delay in connection with the arrangements between Captain
Stockton and the naval authorities at Washington. At length, in 1841,
Captain Stockton was authorized to proceed with the construction of a
screw steam frigate of about one thousand tons. This was the U.S.S.
"Princeton," which marks an epoch as the first screw vessel-of-war. She
was followed by the French "Pomone" in 1843, and the English "Amphion"
in 1844, for the equipment of which Ericsson's agent in England, Count
Von Rosen, received commissions from the French and English governments
respectively.

The "Princeton" was completed in due time and was equipped with two
12-inch wrought-iron guns, one brought by Ericsson from England and one
designed and built under the direction of Captain Stockton. At the
trials of the ship in 1844 the latter gun exploded, killing the
Secretaries of State and of the Navy, besides other prominent visitors
on board, and wounding several others. This terrible disaster threw an
entirely undeserved stigma upon the ship herself and upon Ericsson's
work, and it was not until many years after that his name was entirely
free from some kind of reproach in connection with the "Princeton" and
the deplorable results of the accident on board.

These are some of the principal lines of work with which Ericsson
occupied himself during the twenty-two years between 1839 and 1861. At
the latter date came the supreme opportunity of his life, and his
services in the art of naval construction during the remainder of the
Civil War, which was then in progress, are a part of the history of that
great struggle. Here, as with the propeller, volumes might be written in
the attempt to give a full account of the inception, growth, and final
vindication of Ericsson's ideas regarding naval offence and defence, as
expressed by the means available in the engineering practice of the day.