III. Recent experiments on fog-signals

Abstract

Our most intense coast-lights, including the six-wick lamp, the Wigham gas-light, and the electric light, being intended to aid the mariner in heavy weather, may be regarded, in a certain sense, as fog-signals. But fog, when thick, is intractable to light; the sun annot penetrate it, much less any terrestrial source of illumination. Hence the necessity of employing sound-signals in dense fogs. Bells, ongs, horns, guns, and syrens have been used for this purpose; but t is mainly, if not wholly, explosive signals that I have now to ubmit to the notice of the Society. During the long, laborious, nd, I venture to think, memorable series of observations conducted nder the auspices of the Elder Brethren of the Trinity House at the South Foreland in 1872 and 1873, it was proved that a short 5½-inch owitzer, firing 3 lbs. of powder, yielded a louder report than a long 8-pounder firing the same charge. Here was a hint to be acted n by the Elder Brethren. The effectiveness of the sound depended n the shape of the gun, and as it could not be assumed that in the owitzer we had hit accidentally upon the best possible shape, arrangements were made with the War Office for the construction of a gun pecially calculated to produce the loudest sound attainable from the ombustion of 3 lbs. of powder. To prevent the unnecessary landward aste of the sound, the gun was furnished with a parabolic muzzle, ntended to project the sound over the sea, where it was most needed. The construction of this gun was based on a searching series of experiments executed at Woolwich with small models, provided with muzzles of various kinds. The gun was constructed on the principle of the revolver, its various chambers being loaded and brought in apid succession into the firing position. The performance of the gun roved the correctness of the principles on which its construction was ased. It had been a widely spread opinion among artillerists, that a bronze gun emits a specially loud report. I doubted from the outset whether his would help us, and in a letter dated 22nd April, 1874, ventured o express myself thus :—“The report of a gun, as affecting an observer lose at hand, is made up of two factors—the sound due to the shock of the air by the violently expanding gas, and the sound derived from he vibrations of the gun, which, to some extent, rings like a bell. This latter, I apprehend, will disappear at considerable distances.” The result of subsequent trial, as reported by General Campbell, is, “that the sonorous qualities of bronze are greatly superior to those of cast-iron at short distances, but that the advantage lies with the baser metal at long ranges."