206 FRAGMENTS OF SCIENCE. 
nucleus of sound was a continuous train of echoes, which 
retreated to a continually greater distanc e, 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 23d 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| miles to the N. E. by 
E.; at Brightlingsea, 17^ miles to the N. E. ; and at 
Clacton Wash, 20 miles to the N. E. by 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. how- 
itzer, 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 the instance of Mr. Mackie, who had 
previously gone very thoroughly into the subject, a com- 
mittee of the Elder Brethren visited the cotton-powder 
manufactory, on the banks of the Swale, near Faversham, 
on the 16th of June, 1877. The weights of cotton-powder 
employed were 2 oz., 8 oz., 1 lb., and 2 Ibs., in the form 
of rockets and of signals fired a few feet above the ground. 
The experiments throughout were arranged and conducted 
by Mr. Mackie. Our desire on this occasion was to get 
as near to windward as possible, but the Swale and other 
obstacles limited our distance to 1^ mile. We stood here 
E. S. E. from the firing-point while the wind blew fresh 
from the N. E. 
The cotton-powder yielded a very effective report. The 
rockets in general had a slight advantage over the same 
quantities of material fired near the ground. Theloudness 
of the sound was by no means proportional to the quantity 
of the material exploded, 8 oz. yielding very nearly as loud 
a report as 1 lb. The "aerial echoes," which invariably 
followed the explosion of the rockets, were loud and long- 
continued. 
