The hot air engine, although theoretically recognized for some time
past as the most economical means of converting heat into motive
power, has up to the present met with little success. This is due to
the fact that the arrangement of the motors of this class that have
hitherto been constructed has been such as to render them but slightly
practical. In the Benier hot air engine (illustrated herewith),
however, obstacles that were once considered insurmountable have been
overcome, and the motor presents many advantages over all the types
that have preceded it. Among such advantages we shall cite the
possibility of utilizing air at a high temperature (1,200 or 1,500
degrees), while the rubbing surfaces remain at a moderate temperature
(60 or 80 degrees). The fire grate is placed in the interior of the
cylinder, and is traversed by the cold air forced by a pump. The
expanded hot gases fill the cylinder and act against the piston
directly above the grate.

The type herewith illustrated is of 6 horse power. The motive
cylinder, CC', is bolted to the extremity of the frame, A. Upon this
latter is fixed a column, B, which carries a working beam, E. This
latter transmits the motion of the piston, P, to the shaft, D. A pump,
G, placed within the frame, forces a certain quantity of cold air at
every revolution into the driving cylinder. The piston of this pump is
actuated by the connecting rod, G', jointed to the lever, F', which
receives its motion from the rod, F. A slide valve, _b'_, actuated by
a cam, regulates the entrance of the cold air into the pump during
suction, as well as its introduction into the cylinder. There is a
thrust upon the piston during its upward travel, and an escape of hot
gas through the eduction valve, _h_, during the downward travel.