The outside air-pressure then acted upon it and pushed it down again. In
this down-stroke by air-pressure the work was done. The far end of the
walking-beam was even counter-weighted to help the steam-pressure. The
elastic force of compressed steam was not depended upon, was hardly even
known, in this first working and practical engine of the world. Every
engine of that time was an experimental structure by itself. The boiler,
as we use it, was unknown. Often it was square, stayed and braced
against pressure in a most complicated way. Yet the Newcomen engine held
its place for about seventy-five years; a very long time in our
conception, and in view of the vast possibilities that we now know were
before the science. [Footnote: As late as 1880, the steam-engine
illustrated and described in the "natural philosophy" text books was
still the Newcomen, or Newcomen-Watt engine, and this while that engine
was almost unknown in ordinary circumstances, and double-acting
high-pressure engines were in operation everywhere. This last, without
which not much could be done that is now done, was evidently for a long
time after it came into use regarded as a dangerous and unphilosophical
experiment, hardly scientific, and not destined to be permanently
adopted.]

In the year 1760, James Watt, who was by occupation what is now known as
a model-maker, and who lived in Glasgow, was called upon to repair a
model of a Newcomen engine belonging to the university. While thus
engaged he was impressed with the great waste of steam, or of time and
fuel, which is the same thing, involved in the alternate heating and
cooling of Newcomen's cylinder. To him occurred the idea of keeping the
cylinder as hot as the steam used in it. Watt was therefore the inventor
of the first of those economies now regarded as absolute requirements in
construction. He made the first "steam-jacket," and was, as well, the
author of the idea of covering the cylinder with a coat of wood, or