end of the cylinder to the other, is allowed to escape, by the opening
of a valve, directly into the air. To accomplish this it is evident that
the steam must have an elastic force greater than the pressure of the
air, _or it could not expand and drive out the waste steam on the
other side of the piston, in opposition to the pressure of the air_."
According to this teaching, which the young student is expected to
understand and to entirely believe, a pressure of steam of, say eighty
to a hundred and twenty pounds to the inch on one side of the piston is
accompanied by an absolute vacuum there, which permits the pressure of
the outside air to exert itself against the opposite side of the piston
through the open port at the other end of the cylinder. That is, a state
of things which would exist if the steam behind the piston _were
suddenly condensed_, exists anyway. If it be true the facts should be
more generally known; if not, most of the school "philosophies" need
reviewing.] Then an almost unknown American came upon the scene. In
English hands the story at once passes from this point to the
experiments of Trevethick and George Stevenson with steam as applied to
railway locomotion. But as Watt left it and Trevethick found it, the
steam engine could never have been applied to locomotion. It was slow,
ponderous, complicated and scientific, worked at low pressures, and Watt
and his contemporaries would have run away in affright from the
innovation that came in between them and the first attempts of the
pioneers of the locomotive. This innovation was that of Evans, the
American, of whom further presently.

The first steam-engine ever built in the United States was probably of
the Watt pattern, in 1773. In 1776, the year of beginning for ourselves,
there were only two engines of any kind in the colonies; one at Passaic,
N. J., the other at Philadelphia. We were full of the idea of the
independence we had won soon afterwards, but in material respects we had