s were pushed still further. The gun-cotton near the ground
consisted of 0.5-lb. disks, suspended from a horizontal iron bar about
4.5 feet above the ground.

The rockets carried the same quantity of gun-cotton in their heads,
and the height to which they attained, as determined by a theodolite,
was from 800 to 900 feet. The day was cold, with occasional squalls
of snow and hail, the direction of the sound being at right angles to
that of the wind. Five series of observations were made on board the
'Vestal,' at distances varying from 3 to 6 miles. The mean value of
the explosions in the air exceeded that of the explosions near the
ground by a small but sensible quantity. At Windmill Hill, Gravesend,
however, which was nearly to leeward, and 5.5 miles from the
firing-point, in nineteen cases out of twenty-four the disk fired near
the ground was loudest; while in the remaining five the rocket had the
advantage.

Towards the close of the day the atmosphere became very serene. A few
distant cumuli sailed near the horizon, but the zenith and a vast
angular space all round it were absolutely free from cloud. From the
deck of the 'Galatea' a rocket was discharged, which reached a great
elevation, and exploded with a loud report. Following this solid
nucleus of sound was a continuous train of echoes, which retreated to
a continually greater distance, dying gradually off into silence after
seven seconds' duration. These echoes were of the same character as
those so frequently noticed at the South Foreland in 1872-73, and
called by me 'aerial echoes.'

On the 23rd of March the experiments were resumed, the most noteworthy
results of that day's observations being that the sounds were heard at
Tillingham, 10 miles to the N.E.; at West Mersea, 15.75 miles to the
N.E. by E; at Brightlingsea, 17.5 miles to the N.E.; and at Clacton
Wash, 20.5 miles to the N.E. by 1/2 E. The wind was blowing at the
time from the S.E. Some of these sounds were produced by rockets,
some by a 24-lb. howitzer, and some by an 8-inch Maroon.

In December, 1876, Mr. Gardiner, the managing director of the
Cotton-powder Company, had proposed a trial of this material against
the gun-cotton. The density of the cotton he urged was only 1.03,
while that of the powder was 1.70. A greater quantity of explosive
material being thus compressed into the same volume, Mr. Gardiner
thought that a greater sonorous effect must be produced by the powder.
At th