only been brought into existence, but fully matured. We learn from
it that whereas in the steam engine, on account of the limited range of
temperature in the working cylinder and the rapid conduction of steam
during condensation, no combination of cylinders can materially affect
its present efficiency, internally fired engines, such as gas and
caloric engines--being, as it were, less fettered--can have their
already high efficiency increased by simply overcoming mechanical
difficulties. To this fact is no doubt due the recent remarkable
development of gas and caloric engines. The first caloric or hot air
engine was invented by Sir George Cayley in 1807, and in 1827 Dr. Robert
Stirling, a Scotch minister, took out his first patent for a hot air
engine, which was the foundation of many subsequent machines, and by the
invention of the regenerator he converted what was practically a
scientific toy into an efficient machine.

One of the most ardent workers in this field at the present time is Mr.
James Hargreaves, of Widnes, who, with a thorough theoretical knowledge
of the subject has, after many years of patient perseverance, over come
many of the mechanical difficulties, and designed the engine of which
the above is an illustration.

The sectional elevation, shown in Fig. 1, is an expanded view of the
machine, shown thus to enable the action of the machine to be more
clearly understood; the relative position of the different parts, as
actually made, is shown in the side elevation (Fig. 4). The principal
working parts of the machine are the combustion chamber, D, which is of
the form shown, lined with fire brick, and having an entrance, with the
door screwed down like a manhole lid; the working cylinder, A,
surrounded by the water casing, K; the piston, B, with a water lining,
and coupled to the end of the working beam by a parallel motion, the
beam being supported by two rocking columns, Z, as in engines of the
"grasshopper" type; the air compressor, C, coupled directly to the
piston of the working cylinder; the injection pump, F, for supplying the
fuel--creosote or coal tar--to the combustion chamber; the regenerator
E; the receiver and separator, V Y; the feed and exhaust valves, M.

[Illustration: Fig. 1--SECTIONAL ELEVATION--HARGREAVES' THERMO-MOTOR.]

[Illustration: Fig. 2.]

The action of the machine is as follows: Assuming the engine to be in
condition for starting, the sides of the combustion chamber, D, are