hollow cylinder, perhaps an inch long. He then slips the ring back over the stick as in A (Fig. 8), or he may trim the stick and cylinder as in B or C, previous to readjusting them, to form the shape almost universally in use.

Among the latest devices in the way of whistles are the curious chemical toys made with picrate of potash. When the whistling rockets and fire-pieces first appeared, the whistling was commonly supposed to be produced in the same way as in ordinary whistles, by the air-movements produced by their rapid motion. This is, however, not so. The operation is not at all like that of an air-whistle, but the production of the sound is owing to the peculiar property of picrate of potash of whistling when it is burned. This effect is heard very clearly with that salt when compressed in a tube, and the sonority may be augmented by the addition of various substances. Such a composition may be formed, with no other danger than usually attends the manipulation of explosives, by triturating a mixture of fifteen parts of picrate of potash and one part of Judæan bitumen. Fig. 9—Picrate of Potash Whistle. a, the whistling composition; b, rocket with whistle attached. It is then charged into a pasteboard tube a little less than a half-inch in its interior diameter, and some two and a half inches long (Fig. 9). The tube is closed at one end by a plug of closely tamped clay. The composition is introduced in small charges evenly compressed, till the tube is filled to within about three quarters of an inch of the open end. The whistle may be wired upon the cartridge of a rocket, when it should be furnished with a cap penetrated by a quick match, which, entering the picrated composition, is also inserted into the throat of the rocket, so that the two fire-works shall be inflamed at the same time. The sound of these whistles is sharp at first, and passes gradually, as the tube is emptied of its contents, to a grave tone. By combining the whistles with various devices of fire-works, curious effects are produced, in accordance with which expressive descriptive names have been given to the artifices.

When the picrate whistles were first exhibited at Havre, on the occasion of the Fête nationale, the spectators, irritated at the strident noise they made, and mistaking its origin, exclaimed: "Down with the whistling fellows! duck them!" The enjoyment of the festival was much enhanced when the joke was explained.—Translated for the Popular Science Monthly from La Nature.