While the siren has been adopted and found adequate by the majority of nations, the Canadian Government has installed a far more powerful instrument upon the River St. Lawrence, as the ordinary siren signals originally established near the mouth of the river, although of great power, were found to be inadequate. The new apparatus, which is known as the “diaphone,” gives an extraordinarily powerful sound. It comprises a cylindrical chamber, in the walls of which are cut a number of parallel slits. Concentrically disposed within the chamber is a cylindrical hollow piston, with similar slits and a flange at one end, the whole being enclosed in an outer casing. Air under pressure is admitted into the outer casing, and drives the piston backwards and forwards with great rapidity. The result is that the air effects its escape through the orifices, when they come into line, in intermittent puffs. While the broad principle is not unlike that of the conventional siren, the main difference is that in the latter there is a rotary motion, whereas in the diaphone the action is reciprocating. The great advantage of the latter is that all the vibrations are synchronous, owing to the symmetrical disposition of the slits, and consequently the note produced is very pure. The mechanism is so devised that the piston’s motion is controlled to a nicety, and the sound is constant. Experience has proved that the best results are obtained by using air at a pressure of 30 pounds per square inch. The sound thus produced is intensified to a markedly greater degree by means of a resonator properly attuned. This instrument has displaced the siren among the stations upon the St. Lawrence River. The general type of apparatus has a piston 4½ inches in diameter, and uses 11 pounds of air per second during the sounding of the blast. But at more important stations a far larger and more powerful class of apparatus is used, the diaphone at Cape Race having a piston 8½ inches in diameter and using 27 feet of air per second while sounding. This does not indicate the limit of size, however, since the builders of this terrible noise-producer are experimenting with an apparatus having a piston 14 inches in diameter. The sound issuing from such a huge apparatus would be almost as deafening as the report of a big gun and should succeed in warning a mariner several miles away.