When lightning set a portion of the forest in flames, and caused a multitude of animals or fruits to be roasted, men put it to practical use. They recognised the advantage that fire gave them and sought to preserve it. The retention of the fire which had been sent down from heaven became one of the most weighty and significant of functions. Man learned how to keep wood-fibres smouldering, and how to blow them into flame at will; he also learned that it was possible to convey fire, or the potentiality of fire, along with him in his wanderings. But even then success was uncertain until a lucky chance led him to discover how to produce flames at will, by rubbing two sticks together or by twirling one against the other. These actions were originally performed for other purposes--to bore holes in a piece of wood, or to rub it into fibres; finally, one or the other was carried out with such vigour that a filament began to burn, and the discovery was made. Sparks from flint must have suggested a second method of kindling a fire; certainly the art of igniting soft filaments of wood by means of a spark--thus enabling the very smallest source of combustion to be used for human purposes--was known to man in the earliest times. The obvious results of the use of fire are means of obtaining warmth and of cooking food. [Illustration: ESQUIMAU MAKING FIRE BY FRICTION] [Illustration: AN INGENIOUS INDIAN FIRE DRILL] [Illustration: THE GAUCHO’S WAY OF GETTING A LIGHT] Self-defence had already led to the use of weapons, and, at the same time, the contrivances for hunting and fishing must have become more and more perfect. A very low degree of civilisation is that of races unacquainted with the bow and arrow, and familiar with club or boomerang only--who know how to make use merely of the weight of a substance, or, as in the case of the boomerang, of a peculiar means of imparting motion. The time previous to the discovery of the art of working in metal was the Age of Stone. It was a natural transition period during which men began to learn to make use of the malleable metals, which could be hammered and beaten into various shapes, and finally discovered how to work in iron. Iron, by being placed in the fire, brought to a white heat, and smelted, was rendered capable of being put to such uses as were impossible in the case of brittle materials--bone or stone, for example. Many races never acquired the art of working even in the softer metals, and procured metallic implements from other peoples. The great importance of metal-working is borne out by the fact that the position of the smith, even in legendary times, has been of the utmost significance. The Ages of Stone and of Metal belong to the most important stages of civilisation.