line 1/2 inch from each of the ends.

A lamp hole is cut in the centre, and ventilation holes 1 inch apart, as
shown in Fig. 103. If the latter holes are made square or triangular (base
uppermost), and the metal is cut with a cold chisel so as to leave the side
nearest the edge unsevered, the parts may be turned up to form supports for
the barrel.

[Illustration: FIG. 103.--Plate for lamp chamber cut out ready for
bending.]

The slit lower side of the plate is splayed out into a series of "feet," by
three or more of which, the chamber is secured to the base. Bend the plate
round the barrel and put the two screws and bolts which hold the ends in
place, and tighten them until the barrel is gripped firmly. Screw the
engine to its base, fit on the rubber water connections, and fasten down
the tank by a screw through the centre of the bottom. The screw should pass
through a brass washer, between which and the tank should be interposed a
rubber washer to make a water-tight joint.

The Lamp.--The lamp shown in Fig. 104 was made out of a truncated brass
elbow, a piece of 5/16-inch brass tube, and a round tin box holding about
1/3-pint of methylated spirit. A tap interposed between the reservoir and
burner assists regulation of the flame, and prevents leakage when the lamp
is not in use.

Running the Engine.--The power and displacer cranks must be set exactly
at right angles to one another, and the first be secured by soldering or
otherwise to the crank shaft. The fly wheel will revolve in that direction
in which the displacer crank is 90 degrees ahead of the other.

[Illustration: FIG. l04.-Spirit lamp for hot-air engine, with regulating
tap.]

The packing of the piston should be sufficiently tight to prevent leakage
of air, but not to cause undue friction. When the packing has settled into
place, an occasional drop of oil in the cylinder and guide tube will assist
to make the piston and slide air-tight.

The engine begins to work a quarter of a minute or so after the lamp is
lit, and increases its speed up to a certain point, say 300 revolutions per
minute. When the water becomes very hot it may be changed. The power might
be applied, through demultiplying gear, to a small pump drawing water from
the bottom of the tank and forcing it through the water chamber and a
bent-over stand pipe into the tank again. This will help to keep the water
cool, and will add to the interest of the exhibit by showing "work being
done."