make it fast. Each stop may now be moved 1/16 inch nearer to a
point halfway between them to cause "cushioning" of the piston, by
admitting steam before the stroke is quite finished.

A pump made by the author on this principle, having a 1-1/4 inch stroke and
a 1/2-inch bore, will deliver water at the rate of half a gallon per minute
against a head of a few feet.

Note.--To steady the flow and prevent "water hammer," a small air-chamber
should be attached to the delivery pipe.

An Alternative Arrangement.--If the reader prefers a steam pump which
will work at slow speeds, and be available, when not pumping, for driving
purposes, the design may be modified as shown diagrammatically in Fig. 114.
The striker becomes a cross head, and is connected by a forked rod passing
on each side of the pump with the crank of a fly wheel overhanging the
base. The valve is operated in the ordinary manner by an eccentric on the
crankshaft. The steadying effect of the fly wheel and the positive action
of the valve make it possible to use a larger pump plunger than is
advisable with the striking gear. With a pump piston of considerably
greater diameter than the piston rod, the pump may be made double-acting, a
gland being fitted at the front end for the piston rod to work through,
and, of course, a second set of valves added.

[Illustration: Fig. 114.--Plan of steam pump with fly wheel.]

A SUGGESTION.

For exhibition purposes a small, easily running, double-action pump might
be worked by the spindle of a gramophone. A crank of the proper throw and a
connecting rod must be provided. Both delivery pipes feed, through an
air-chamber, a fountain in the centre of a bowl, the water returning
through an overflow to the source of supply, so that the same water may be
used over and over again.

XXIII. KITES.

Plain Rectangular Box Kites.--The plain box kite is easy to make and a
good flier. Readers should try their hands on it before attempting more
complicated models.

Lifting pressure is exerted only on the sides facing the wind, but the
other sides have their use in steadying the kite laterally, and in holding
in the wind, so that they justify their weight.

Proportions of Box.--Each box has wind faces one and a third times as
long as the sides, and the vertical depth of the box is about the same as
its fore and aft dimensions. That is, the ends of the boxes are square, and
the wind faces oblong, with one-third as much area ag