alert as they are, will not, it might be
presumed, be able to slip from condensation to rarefaction with a
rapidity sufficient to forestall the formation of the wave. On _a
priori_ grounds then, we are entitled to infer the effectiveness of
gun-cotton, while in a great number of comparative experiments,
stretching from 1874 to the present time, this inference has been
verified in the most conclusive manner.

As regards explosive material, and zealous and accomplished help in
the use of it, the resources of Woolwich Arsenal have been freely
placed at the disposal of the Elder Brethren. General Campbell,
General Younghusband, Colonel Fraser, Colonel Maitland, and other
officers, have taken an active personal part in the investigation, and
in most cases have incurred the labour of reducing and reporting on
the observations. Guns of various forms and sizes have been invoked
for gunpowder, while gun-cotton has been fired in free air and in the
foci of parabolic reflectors.

On the 22nd of February, 1875, a number of small guns, cast specially
for the purpose--some with plain, some with conical, and some with
parabolic muzzles--firing 4 oz. of fine-grain powder, were pitted
against 4 oz. of gun-cotton detonated both in the open, and in the
focus of a parabolic reflector. [Footnote: For charges of this
weight the reflector is of moderate size, and may be employed without
fear of fracture.]

The sound produced by the gun-cotton, reinforced by the reflector, was
unanimously pronounced loudest of all. With equal unanimity, the
gun-cotton detonated in free air was placed second in intensity.
Though the same charge was used throughout, the guns differed notably
among themselves, but none of them came up to the gun-cotton, either
with or without the reflector. A second series, observed from a
different distance on the same day, confirmed to the letter the
foregoing result.

As a practical point, however, the comparative cost of gun-cotton and
gunpowder has to be taken into account, though considerations of cost
ought not to be stretched too far in cases involving the safety of
human life. In the earlier experiments, where quantities of equal
price were pitted against each other, the results were somewhat
fluctuating. Indeed, the perfect manipulation of the gun-cotton
required some preliminary discipline--promptness, certainty, and
effectiveness of firing, augmenting as experience increased. As 1 lb.
of gun-cotton costs