he principles which guide
the scientific development of the steam engine. His words are:

"My method of lessening the consumption of steam, and
consequently fuel, in fire engines, consists of the following
principles:

"First, That vessel in which the powers of steam are to be
employed to work the engine, which is called the cylinder in
common fire engines, and which I call the steam vessel, must,
during the whole time the engine is at work, be kept as hot as
the steam that enters it; first, by enclosing it in a case of
wood, or any other materials that transmit heat slowly;
secondly, by surrounding it with steam or other heated bodies;
and, thirdly, by suffering neither water nor any other substance
colder than the steam to enter or touch it during that time.

"Secondly, In engines that are to be worked wholly or partially
by condensation of steam, the steam is to be condensed in
vessels distinct from the steam vessels or cylinders, although
occasionally communicating with them; these vessels I call
condensers; and, whilst the engines are working, these
condensers ought at least to be kept as cold as the air in the
neighborhood of the engines, by application of water or other
cold bodies.

"Thirdly, Whatever air or other elastic vapor is not condensed
by the cold of the condenser, and may impede the working of the
engine, is to be drawn out of the steam vessels or condensers by
means of pumps, wrought by the engines themselves, or otherwise.

"Fourthly, I intend in many cases to employ the expansive force
of steam to press on the pistons, or whatever may be used
instead of them, in the same manner in which the pressure of the
atmosphere is now employed in common fire engines. In cases
where cold water cannot be had in plenty, the engines may be
wrought by this force of steam only, by discharging the steam
into the air after it has done its office....

"Sixthly, I intend in some cases to apply a degree of cold not
capable of reducing the steam to water, but of contracting it
considerably, so that the engines shall be worked by the
alternate expansion and contraction of the steam.

"Lastly, Instead of using water to render the pistons and other
parts of the engine air and steam tight, I employ oils, wax,
resinous bodies, fat of animals, quick-silver and other met