106 REPORT—1863. 
are conflicting, and there is scarcely one fact relating to its use as a signal. 
which can be considered as established. Even the most important of all, the 
distance at which it ceases to be heard, is undecided. But it is the more 
necessary on this account to lose no time in obtaining results which shall 
come with such authority that they may command respect and acquiescence. 
“Up to the present time all signal-sounds have been made in air, though 
this medium has grave disadvantages: its own currents interfere with the 
sound-waves, so that a gun or bell which is heard several miles down the 
wind is inaudible at more than a few furlongs wp it. A still greater evil is 
that it is least effective when most needed; for fog is a powerful damper of 
sound: it is a mixture of air and globules of water, and at each of the innu- 
merable surfaces where these two touch, a portion of the vibration is reflected 
and lost. This has a familiar illustration in a glass of champagne, which 
when struck will only give a dull sound while effervescing, but rings clearly 
when the gas has escaped. Snow produces a similar effect, and one still 
more injurious. 
‘‘ Water transmits sound with great power, and seems to possess in some 
other respects a decided superiority over air, but has been so little studied 
in this point of view that we can neither pronounce on the best mode of 
applying its powers or the practical difficulties which we may have to 
encounter. 
«“ The signal which (judging from the Report referred to) is most approved 
by sailors is a gun stationed at or near the danger, and fired at intervals, 
mostly of half an hour; in the case of the Holyhead mail-steamers, of fifteen 
minutes, when they are expected, The gun must be heavy, and the cost of 
ammunition is about £200 a year. The Holyhead gun is said to be ‘ heard 
in all weathers at Skerries, nine miles off ;’? but this distance is greater than 
any other which appears in the evidence. It must be remarked that half- 
hour intervals are much too long for rapid steamers, which in that time might 
run seyen or eight miles—a space through which the gun could not be heard 
in thick fog. Against gun-signals there are also the objections that they de- 
pend on the punctuality of the signal-men, and that they are often fired by 
ships in distress. 
«Bells and gongs are also extensively used ; but we have no exact infor- 
mation as to the proper size, the force of blow required, or the distance at 
which they can be relied on. In many cases they have been abandoned for 
guns. The most effective one described is at the Copeland Light, in Belfast 
Lough, which is tolled by machinery, and is stated to have been heard at 
thirteen miles’ distance. But it must be noted that this very spot is notorious 
for wrecks in foggy weather ; so that even this powerful bell is of little avail. 
The gong of the Warner has been heard at the Nab, three miles off; but 
several instances are given where bells or gongs could not be heard at a 
quarter of a mile. The gong is said to be heard best down the wind, the 
bell wp it. An ingenious contrivance to intensify the sound of a bell, and at 
the same time to send it in a given direction, has been tried at Boulogne : the 
bell is put in the focus of a parabolic reflector made of mason-work, which 
ought to concentrate the sound in the direction of its axis. It seems not to 
have succeeded well; the sound-rays diffuse more than those of light, and 
probably the reflexion is imperfect. On the whole, the evidence leaves an 
impression on the mind that sounds excited by percussion cannot universally 
be trusted for half a mile. Drums seem not to have been tried. 
«The third class of signals is made by wind instruments, including in that 
category those blown by steam, These seem the most promising, but their 
