orifice in the bottom of the same size.

CALCULATING FUEL ENERGY.--Power from fuels depends upon the expansion of
the materials consumed, or upon the fact that heat expands some element,
like water, which in turn produces the power. One cubic inch of water,
when converted into steam, has a volume equal to one cubic foot, or
about 1,700 times increase in bulk.

Advantage is taken of this in steam engine construction. If a cylinder
has a piston in it with an area of 100 square inches, and a pipe one
inch square supplies steam at 50 pounds pressure, the piston will have
50 pounds pressure on every square inch of its surface, equal to 5,000
pounds.

THE PRESSURE OR HEAD.--In addition to that there will also be 50 pounds
pressure on each square inch of the head, as well as on the sides of the
cylinder.

Fig. 131 shows a cylinder (A), a piston (B) and a steam inlet port (C),
in which is indicated how the steam pressure acts equally in all
directions. As, however, the piston is the only movable part, the force
of the steam is directed to that part, and the motion is then
transmitted to the crank, and to the shaft of the engine.

[Illustration: _Fig. 131. Steam Pressure_]

[Illustration: _Fig. 132. Water Pressure_]

This same thing applies to water which, as stated, is dependent on its
head. Fig. 132 represents a cylinder (D) with a vertically movable
piston (E) and a standpipe (F). Assuming that the pipe (F) is of
sufficient height to give a pressure of 50 pounds to the square inch,
then the piston (E) and the sides and head of the cylinder (D) would
have 50 pounds pressure on every square inch of surface.

FUELS.--In the use of fuels, such as the volatile hydrocarbons, the
direct expansive power of the fuel gases developed, is used to move the
piston back and forth. Engines so driven are called _Internal Combustion
Motors_.

POWER FROM WINDS.--Another source of power is from the wind acting
against wheels which have blades or vanes disposed at such angles that
there is a direct conversion of a rectilinear force into circular
motion.

In this case power is derived from the force of the moving air and the
calculation of energy developed is made by considering the pressure on
each square foot of surface. The following table shows the force exerted
at different speeds against a flat surface one foot square, held so that
the wind strikes it squarely:

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