t all the heat generated
and apply it to this purpose. But if we express this quantity of heat in
its mechanical equivalent, and suppose that we could get the corresponding
quantity of work out of our pound of coal, we should be grievously
mistaken. For in the first place, we could not collect all the heat given
out, because a great deal is communicated to the products of combustion by
which it is absorbed, and locked up in a form that renders it incapable of
measurement by our thermometers. In the next place, if we make an
allowance for the quantity of heat which thus disappears, even then the
corrected calorific power converted into its mechanical equivalent would
not express the quantity of work practically obtainable from the coal.

In the most perfectly constructed engine the whole amount of heat
generated by the combustion of the coal is not available for heating the
boiler--a certain quantity is lost by radiation, by heating the material
of the furnace, &c., by being carried away by the products of combustion
and in other ways. Moreover, some of the coal escapes combustion by being
allowed to go away as smoke, or by remaining as cinders. Then again, in
the engine itself a good deal of heat is lost through various channels,
and much of the working power is frittered away through friction, which
reconverts the mechanical power into its equivalent in heat, only this
heat is not available for further work, and is thus lost so far as the
efficiency of the engine is concerned. These sources of loss are for the
most part unavoidable, and are incidental to the necessary imperfections
of our mechanism. But even with the most perfectly conceivable constructed
engine it has been proved that we can only expect one-sixth of the total
energy of the fuel to appear in the form of work, and in a very good
steam-engine of the present time we only realize in the form of useful
work about one-tenth of the whole quantity of energy contained in the
coal. Although steam power is one of the most useful agencies that science
has placed at the disposal of man, it is not generally recognized by the
uninitiated how wasteful we are of Nature's resources. One of the greatest
problems of applied science yet to be solved is the conversion of the
energy latent in coal or other fuel into a quantity of useful work
approximating to the mechanical equivalent much more closely than has
hitherto been accomplished.

But although we only get this small