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Fire.   17 3

to burn. The vestal fire of Rome and the sacred fire of the Mexicans were obtained by means of reflectors. If I understand aright, they consisted of a stone with a conical hollow, carefully polished, the apex of the hollow cone was a right angle : the tinder was held in the axis of the cone. See Tylor's `Early History of Mankind.'

Black Tinder.-Tinder that is black by previous charring, or from any other cause, ignites in the sun far sooner than light-coloured tinder.

Fire by conversion of motion into heat.-General Remarks.When a moving body is arrested, heat is given out ; the quantity of heat being in exact proportion to the mass, multiplied into the square of its velocity. Thus if a cannon ball be fired at an iron target, both it and the ball become exceedingly hot. There is even a flash of light when the velocity of the ball is very high. When bullets are fired with heavy charges at a target, the lead is just melted by the heat of impact, and it " splashes," to use a common phrase. It is obvious from these two examples, that no velocity which the hand of man is able to give to a steel, when striking a flint, or to one stick rubbing against another stick, will be competent to afford a red-hot temperature unless the surface against which impact or friction is made be very small, or unless great care be taken to avoid the wasteful dissipation of heat. The spark made by a flint and steel, consists of a thin shaving of steel, scraped off by the flint and heated by the arrested motion. When well struck, the spark is white-hot and at that temperature it burns with bright scintillations in the air, just as iron that is merely red-hot burns in pure oxygen. This is the theory:. now for the practice.

Flints.-If we may rely on a well-known passage in Virgil, concerning IEneas and his comrades, fire was sometimes made in ancient days by striking together two flints, but I confess myself wholly unable to light tinder with flints alone, and I am equally at a loss to understand what were the "dry leaves " that they are said in the same passage to have used for tinder. Neither can I obtain fire except with a flint and steel, or, at least, hardened iron; a flint and ordinary iron will not give an available spark. Flints may be replaced by any