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 making of fire.  The contrivances for obtaining fire are many and curious in savage life, while, once attained, this art seems to have not only formed a constant accompaniment but probably also a determining cause in the evolution of civilization.  Wood, the fat of animals, and even the oils expressed from plants, probably all became known to man as convenient sources of fuel in prehistoric times.  From the incineration of wood to the use of peat and coal would prove an easy stage in the advance toward present day practices, and with the attainment of coal as a fuel the first great era in man’s fire-making habits may be said to end.

Beyond the coal stage, however, lies the more or less distinctively modern one of the utilization of gas and oil for fuel.  The existence of great natural centers, or underground stores, of gas and oil is probably no new fact.  We read in the histories of classic chroniclers of the blazing gases which were wont to issue from the earth, and to inspire feelings of superstitious awe in the minds of beholders.  Only within a few years, however, have geologists been able to tell us much or anything regarding these reservoirs of natural fuel which have become famous in America and in the Russian province of Baku.