preserve the sacred fire, which if once extinguished, it was thought would bring ruin and destruction upon their city. [Illustration: Fig. 1.] How did our ancestors, think you, obtain fire in those early times? I suggested a burning mountain as a source of fire. You remember, too, perhaps reading about Prometheus, who stole fire from heaven, bringing it to earth in a copper rod, which combined act of theft and scientific experiment made the gods very angry, because they were afraid mortals might learn as many wonderful things as they knew themselves. History seems to show that the energetic rubbing together of dry sticks was one of the earliest methods adopted by our ancestors for producing fire. I find, for instance, described and pictured by an early author some such plan as the following:--A thick piece of wood was placed upon the ground. Into a hole bored in this piece of wood a cone of wood was fitted. By placing a boy or man on the top of the cone, and whirling him round, sufficient friction resulted where the two pieces of wood rubbed one against the other to produce fire. Our artist has modernized the picture to give you an idea of the operation (Fig. 1). Now instead of repeating that experiment exactly, I will try to obtain fire by the friction of wood with wood. I take this piece of boxwood, and having cut it to a point, rub it briskly on another piece of wood (Fig. 2). If I employ sufficient energy, I have no doubt I may make it hot enough to fire tinder. Yes! I have done so, as you see. (I will at once apologize for the smoke. Unfortunately we cannot generally have fire without smoke.) Every boy knows that experiment in another form. A boy takes a brass button, and after giving it a good rub on his desk, applies it to the cheek of some inoffensive boy at his side, much to the astonishment of his quiet neighbour. Well, I am going to see whether I can produce fire with a brass button. I have mounted my button, as you see, for certain reasons on a cork, and I will endeavour by rubbing the button on a piece of pinewood to make it sufficiently hot to fire tinder. Already I have done so. [Illustration: Fig. 2.] Talking about friction as a means of producing heat, I should like to mention that at the last Paris Exhibition I saw water made to boil, and coffee prepared from it, by the heat resulting from the friction of two copper plates within the liquid.