analogous case, "the dissipation of energy," has formed the subject of
more than one learned essay.

Before the invention of the steam-engine, the only powers employed in
mechanics were those of wind and water mills, and animal power. In the
first two, no conversion of one force into another took place; they
were mere kinematic devices for employing the mechanical force already
existing in the gale of wind and the head of water. With regard to the
power developed by man and other animals, we had in them examples of
most efficient heat-engines, converting into power a large percentage
of the fuel burnt in the lungs. But animal power is small in amount,
and it is expensive for two reasons--first, because the agents require
long intervals of rest, during which they still burn fuel; and next,
because the fuel they require is very expensive. A pound of bread or
beef, or oats or beans, costs a great deal more than a pound of coal;
while it does not, by its combustion, generate nearly so much heat.
The steam-engine, therefore, took the place of animal power, and for a
long time stood alone; and nearly all the motive power derived from
heat is still produced by the mechanism which Watt brought to such
great efficiency in so short a time.

Now the practical question for all designers and employers of
heat-engines is to determine how the greatest quantity of motive force
can be developed from the heat evolved from a given kind of fuel; and
coal being the cheapest of all, we will see what are the results
obtainable from it by the steam-engine. In this we have three
efficiencies to consider--those of the furnace, the boiler, and the
cylinder.

First, with respect to the furnace. The object is to combine the