We might make a distinct and legitimate study of numerous forms of sounding apparatus, constructed on the theory of the whistle, whose peculiarities consist in the manner in which the air is sent over the tongue, the vibration of which produces the sound. Thus, we have the pedal-horn, and the India-rubber bulb whistle of tramways and omnibuses, the various systems of horns that give notice of the approach of fire-engines, the alarm whistles of steam-engines, "howler" whistles, and locomotive whistles; the last of which are sometimes tuned to nearly a distinct tone for each line. Much that is interesting might also be said concerning the variations in the engineer's whistle for his different calls, upon the signal-man, for the clearance of the track, etc. But this would take us away from our topic.
Modern common whistles are infinite in their variety, and new kinds are appearing every day, as the fancies of amateurs bring them forth. They are made of wood, bark, metal, horn, shell, glass, and even of sugar. While the form of the apparatus and the manner of using it change from time to time, as the fruitful imaginations of fanciers devise new patterns, the principle of the construction is invariable. Some conception of the capabilities in design of the instrument may be gained from a glance at Fig. 4. Among the whistles here represented, we find the scholar whistle (3), the fireman's whistle (5), which gives mi when the upper hole is open, and do when it is closed with the finger; the Belgian whistle (15), of inelegant shape; the square whistle with two holes, giving two notes (7); and the Baduel army regulation whistle (9), Of a quite different type is the Swiss whistle for railroad-station agents (2), in which the column of air is broken upon the summit sphere and a part is swallowed up, while another part is thrown outside. The marine regulation whistle (6) is of a similar structure; but, like the American whistle, there is a secret in manipulating it. In order to produce a sound, the upper end of the pipe and the adjacent sphere must be shut up in the hand. A variety of movements are necessary for the execution of different modulations, which make a whistling-school on the quarter-deck the analogue of the schools of the trumpet and the drum in regiments. There are also whistles with three or four openings, like the horn whistle and the railroad whistle. In the former (13) the extremities A and D may be regarded as mouths, and the sounds are also modified by closing alternately or in succession the openings B and C. In the second (13), by leaving all open, we obtain a quite characteristic mixed and false sound. Special modifications are obtained with the roulette whistle (1) and the bird whistle, with which the songs of various birds are imitated. Fancy has run rife in devising typical whistles, like
