284 Report on the Trials of Reaping Macltines at Leamington, 
annulus all around the bottom. Within this heater is the- 
telescope G, which is a thin iron cylinder, about one-fourth of 
an inch less in diameter than the interior of the heater. It is 
fitted to the interior of the power-cylinder B, and extends nearly 
to the bottom of the heater. Its office is to cause the air which 
flows from the compression-cylinder to be presented in a thin 
sheet all around the interior surface of the heater, and par- 
ticularly at the lower and hotter portion. By this means the 
air is thoroughly and rapidly heated. The same air is used 
continuously, as there is neither influx nor escape, the air being 
merely shifted from one cylinder to the other. Between the 
compression and power-cylinders is situated the regenerator H, 
the economical value of which cannot be overrated. This 
regenerator is composed of a number of thin plates, slightly 
thickened at their edges, which, while affording a free passage 
to the air, subdivides it into thin sheets. It is so placed 
between the cylinders as to be traversed by the air in its- 
passage each way between the hot and cold cylinders. Thus 
the heat is alternately abstracted from and returned to the air 
in its passage backwards and forwards through these plates, 
imparting great economy and steadiness of power to the engine. 
The other portions of the engine are readily understood on 
inspection of the cut. The two pistons are attached directly 
to the crank 1 1 (which stand at an angle of about 95° from 
each other, the crank of the power-piston being in advance), by 
simple connecting rods, J J ; and all the movements of the 
various parts are uniform, being solely derived from regular, 
circular, and rectilinear motion ; and as there are no com- 
plicated parts, and none of the irregular intermittent impulses 
which characterise caloric engines, a high rate of speed and 
smooth action may be safely and easily obtained. K K are the 
packings which are in duplicate for each cylinder. The lower 
one has its lap downwards to resist the escape of air below the 
piston, while the upper one has its lap upwards to prevent the 
lubricating material from entering too freely into the cylinders. 
Between them is the relief- ring, which is so constructed as to 
almost entirely relieve the friction of the packings. L is a 
simple check-valve which supplies any slight leakage of air 
which may occur. It is generally placed at the back of the 
engine, at the lower part of the compression-cylinder, but is 
necessarily shown in the sectional cut on the side. 
The operation of the engine is briefly as follows : — 
The compression-piston C first compresses the cold air in the 
lower part of the compression-cylinder A into about one-third 
its normal volume, when, by the advancing or upward motion 
of the power-piston D, and the completion of the down-strok 
