The construction of this very powerful means of communicating intelligence by sound is shown in the annexed Fig.; it is all of brass, and the foot a is cast hollow with a flanch b at the bottom, to bolt it upon the fire-box; it has a cock c placed in it with the handle d and screw e to keep it tight; the handle projecting out to allow firm hold to be taken of it. The cup fis fixed upon the foot a by screwing the piece g upon it, and both are turned truly at their outer edges, leaving a very narrow passage i i between them all round. The piece g is hollow, having holes h in its sides, and a pillar k stands upon its centre, on which is screwed the bell l l; the thin edge of which is brought just over the opening i, and half an inch above it. When the cock is opened, the steam enters the cup f through the holes h, and rushes out at the narrow slit i, striking the thin edge of the bell l, in a similar manner to the action in organ pipes, and producing an exceedingly shrill sound: some holes m are made in the top of the bell, to allow the steam to pass freely through, which improves the sound considerably. The cock is required to be steadily opened to adjust the quantity of steam, so as to produce the clearest sound.
The steam whistle is very effective, and its sound can be heard at a great distance.