stle, the 'Iron Duke' and 'Vanguard' need never have come into
collision.

It was the necessity of providing a suitable signal for rock
lighthouses, and of clearing obstacles which cast an acoustic shadow,
that suggested the idea of the gun-cotton rocket to Sir Richard
Collinson, Deputy Master of the Trinity House. His idea was to place
a disk or short cylinder of gun-cotton in the head of a rocket, the
ascensional force of which should be employed to carry the disk to an
elevation of 1000 feet or thereabouts, where by the ignition of a fuse
associated with a detonator, the gun-cotton should be fired, sending
its sound in all directions vertically and obliquely down upon earth
and sea. The first attempt to realise this idea was made on July 18,
1876, at the firework manufactory of the Messrs. Brock, at Nunhead.
Eight rockets were then fired, four being charged with 5 oz. and four
with 7.5 oz. of gun-cotton. They ascended to a great height, and
exploded with a very loud report in the air. On July 27, the rockets
were tried at Shoeburyness.

The most noteworthy result on this occasion was the hearing of the
sounds at the Mouse Lighthouse, 8.5 miles E. by S, and at the Chapman
Lighthouse, 8.5 miles W. by N; that is to say, at opposite sides of
the firing-point. It is worthy of remark that, in the case of the
Chapman Lighthouse, land and trees intervened between the firing-point
and the place of observation. This,' as General Younghusband justly
remarked at the time, 'may prove to be a valuable consideration if it
should be found necessary to place a signal station in a position
whence the sea could not be freely observed.' Indeed, the clearing of
such obstacles was one of the objects which the inventor of the rocket
had in view.

With reference to the action of the wind, it was thought desirable to
compare the range of explosions produced near the surface of the earth
with others produced at the elevation attainable by the gun-cotton
rockets. Wind and weather, however, are not at our command; and hence
one of the objects of a series of experiments conducted on December
13, 1876, was not fulfilled. It is worthy, however, of note that on
this day, with smooth water and a calm atmosphere, the rockets were
distinctly heard at a distance of 11.2 miles from the firing-point.
The quantity of gun-cotton employed was 7.5 oz. On Thursday, March 8,
1877, these comparative experiments of firing at high and low
elevation