2 inches by 6 inches.

The numbers under the respective weights express the recorded value of
the sounds. They must be simply taken as a ready means of expressing
the approximate relative intensity of the sounds as estimated by the
ear. When we find a 9-oz. charge marked 4, and a 12-oz. charge marked
4.03, the two sounds may be regarded as practically equal in
intensity, thus proving that an addition of 30 per cent. in the
larger charges produces no sensible difference in the sound. Were the
sounds estimated by some physical means, instead of by the ear, the
values of the sounds at the distances recorded would not, in my
opinion, show a greater advance with the increase of material than
that indicated by the foregoing numbers. Subsequent experiments
rendered still more certain the effectiveness, as well as the economy,
of the smaller charges of gun-cotton.

It is an obvious corollary from the foregoing experiments that on our
'nesses' and promontories, where the land is clasped on both sides for
a considerable distance by the sea--where, therefore, the sound has to
propagate itself rearward as well as forward--the use of the parabolic
gun, or of the parabolic reflector, might be a disadvantage rather
than an advantage. Here guncotton, exploded in the open, forms the
most appropriate source of sound. This remark is especially
applicable to such lightships as are intended to spread the sound all
round them as from central foci.

As a signal in rock lighthouses, where neither syren, steam-whistle,
nor gun could be mounted; and as a handy fleet-signal, dispensing with
the lumber of special signal-guns, the gun-cotton will prove
invaluable. But in most of these cases we have the drawback that
local damage may be done by the explosion. The lantern of the rock
lighthouse might suffer from concussion near at hand, and though
mechanical arrangements might be devised, both in the case of the
lighthouse and of the ship's deck, to place the firing-point of the
gun-cotton at a safe distance, no such arrangement could compete, as
regards simplicity and effectiveness, with the expedient of a
gun-cotton rocket. Had such a means of signalling existed at the
Bishop's Rock lighthouse, the ill-fated 'Schiller' might have been
warned of her approach to danger ten, or it may be twenty, miles
before she reached the rock which wrecked her. Had the fleet
possessed such a signal, instead of the ubiquitous but ineffectual
whi