Processes that are based upon the clashing of two flint stones must be much more inconvenient of application than we would be led to suppose. We are, in fact, accustomed to see the flint and steel used, but here the spark is a bit of iron raised to red heat through a mechanical action that has violently detached it from the mass under the form of a small sliver. In the case of two flint stones, the light that is perceived is of an entirely different nature, for it is a phosphorescence which is produced, even by a very slight friction, not only between two pieces of silex, but also between two pieces of quartz, porcelain, or sugar; and that the heat developed is but slight is proved by the fact that the phenomenon may occur under water. Of course, fragments of stones may be raised to a red heat through percussion; but this does not often occur, so for this reason the Fuegians keep up with the greatest care the fires that they have lighted, and it is this very peculiarity that has given their country a characteristic aspect and caused it to be named Terra del Fuego (land of fire). When they change their residence they always carry with them a few lighted embers which rest in their canoes upon a bed of pebbles or ashes. The same thing occurs, moreover, among the Australians and Tasmanians, who employ, as we have just seen, the rotary process. There are women among these peoples whose special mission it is to carry day and night lighted torches or cones made of a substance that burns slowly like punk. When, through accident, the fire happens to get extinguished in a tribe, these people often prefer to undertake a long voyage in order to obtain another light from a neighboring tribe rather than have recourse to a direct production of it. We can understand from what is still taking place in these distant countries why the worship of fire should have existed among our ancestors, and why sacerdotal associations, such as the Brahmins of India, the Guebers of Persia, the Vestals of Rome, the priests of Baal in Chaldea and Phenicia should have been specially instituted for producing and preserving it. Plutarch narrates (Numa, chap. ii.) that when the sacred fire happened to go out, there was employed for relighting it a brass mirror that had the form of a cone generated by the hypothenuse of an isosceles rectangular triangle revolving around one of the sides of the right angle. [Illustration: FIG. 4.--NATIVE OF OCEANICA OBTAINING FIRE BY FRICTION.]