ief, and, indeed, the only substance which falls
to be considered under the name of fuel. In other countries, however,
the case is different. Various materials, ranging from wood to oil,
come within the category of material for the production of heat. The
question of fuel, it may be remarked, has a social, an antiquarian,
and a chemical interest. In the first place, the inquiry whether or
not our supplies of coal will hold out for say the next hundred
thousand years, or for a much more limited period only, has been very
often discussed by sociologists and by geological authorities.

Again, it is clear that as man advances in the practice of civilized
arts, his dependence upon fuel becomes of more and more intimate
character. He not merely demands fire wherewith to cook his food, and
to raise his own temperature or that of his dwelling, but requires
fuel for the thousand and one manufacturing operations in which he is
perpetually engaged. It is obvious that without fuel civilized life
would practically come to an end. We cannot take the shortest journey
by rail or steamboat without a tacit dependence upon a fuel supply;
and the failure of this supply would therefore mean and imply the
extinction of all the comforts and conveniences on which we are
accustomed to rely as aids to easy living in these latter days. Again,
socially regarded, man is the only animal that practices the
fire-making habit. Even the highest apes, who will sit round the fire
which a traveler has just left, and enjoy the heat, do not appear to
have developed any sense or idea of keeping up the fire by casting
fresh fuel upon it. It seems fairly certain, then, that we may define
man as being a "fuel-employing animal," and in so doing be within the
bounds of certitude. He may be, and often is, approached by other
animals in respect of many of his arts and practices. Birds weave nest
materials, ants make--and maul--slaves, beavers build dams, and other
animals show the germs and beginnings of human contrivances for aiding
the processes of life, but as yet no animal save man lights and
maintains a fire. That the fire-making habit must have dawned very
early in human history appears to be proved by the finding of ashes
and other evidences of the presence of fire among the remains and
traces of primitive man.

All we know, also, concerning the history of savage tribes teaches us
that humanity is skillful, even in very rude stages of its progress,
in the m