the contact between the gases and the heating surfaces of the boiler,
nearly half of the heat of the fire was lost. With a view to overcoming
this loss at least partially, he used an internal furnace with a smoke
flue winding through the water in the form of a worm in a still. In
order that the length of passage of the gases might not act as a damper
on the fire, Dr. Allen recommended the use of a pair of bellows for
forcing the sluggish vapor through the flue. This is probably the first
suggested use of forced draft. In forming an estimate of the quantity of
fuel lost up the stack, Dr. Allen probably made the first boiler test.

Toward the end of the period of use of Newcomen's atmospheric engine,
John Smeaton, who, about 1770, built and installed a number of large
engines of this type, greatly improved the design in its mechanical
details.

[Illustration: Erie County Electric Co., Erie, Pa., Operating 3082 Horse
Power of Babcock & Wilcox Boilers and Superheaters, Equipped with
Babcock & Wilcox Chain Grate Stokers]

The improvement in boiler and engine design of Smeaton, Newcomen and
their contemporaries, were followed by those of the great engineer,
James Watt, an instrument maker of Glasgow. In 1763, while repairing a
model of Newcomen's engine, he was impressed by the great waste of steam
to which the alternating cooling and heating of the engine gave rise.
His remedy was the maintaining of the cylinder as hot as the entering
steam and with this in view he added a vessel separate from the
cylinder, into which the steam should pass from the cylinder and be
there condensed either by the application of cold water outside or by a
jet from within. To preserve a vacuum in his condenser, he added an air
pump which should serve to remove the water of condensation and air
brought in with the injection water or due to leakage. As the cylinder
no longer acted as a condenser, he could maintain it at a high
temperature by covering it with non-conducting material and, in
particular, by the use of a steam jacket. Further and with the same
object in view, he covered the top of the cylinder and introduced steam
above the piston to do the work previously accomplished by atmospheric
pressure. After several trials with an experimental apparatus based on
these ideas, Watt patented his improvements in 1769. Aside from their
historical importance, Watt's improvements, as described in his
specification, are to this day a statement of t