other non-conductor. He contrived a second chamber, outside of the
cylinder, where the then indispensable condensation should take place.
Then he gave this cylinder for the first time two heads, and let out the
piston-rod through a hole in the upper head, with packing. He used steam
on the upper side of the piston as well as the lower, and it will be
seen that he came very near to making the modern engine.

Yet he did not make it. He was still unable to dispense with the
condensing and vacuum and air-pressure ideas. Acting for the first time
in the line of real efficiency, he failed to go far enough to attain it.
He made a double-acting engine by the addition of many new parts; he
even attained the point of applying his idea to the production of
circular motion. But he merely doubled the Newcomen idea. His engine
became the Newcomen-Watt. He had a condensing chamber at each end of the
stroke and could therefore command a reciprocating movement. The
walking-beam was retained, not for the purpose for which it is often
used now, but because it was indispensable to his semi-atmospheric
engine.

[Illustration: THE PERFECTED NEWCOMEN-WATT ENGINE.]

It may seem almost absurd that the universal crank-movement of an engine
was ever the subject of a patent. Yet such was the case. A man named
Pickard anticipated Watt, and the latter then applied to his engines the
"sun-and-planet" movement, instead of the crank, until the patent on the
latter expired. The steam-engine marks the beginning of a long series of
troubles in the claims of patentees.

In 1782 came Watt's last steam invention, an engine that used steam
_expansively_. This was an immense stride. He was also at the same