208 FRAGMENTS OF SCIENCE. 
others, containing similar quantities of cotton-powder, 
had been supplied by the Cotton-powder Company at 
Faversham. With these were compared the ordinary 
18-pounder gun, which happened to be mounted at 
Dungeness, firing the usual charge of 3 Ibs. of powder, 
and a syren. 
From these experiments it appeared that the gun-cotton 
and cotton-powder were practically equal as producers of 
sound. 
The effectiveness of small charges was illustrated in a 
very striking manner, only a single unit separating the 
numerical value of the 8-oz. rocket from that of the 2-oz. 
rocket. The former was recorded as 6.9 and the latter as 
5.9, the value of the 4-oz. rocket being intermediate be- 
tween them. These results were recorded by a number of 
very practiced observers on board the Galatea. They were 
completely borne out by the observations of the Coastguard 
who marked the value of the 8-oz. rocket 6.1, and that of 
the 2-oz. rocket 5.2. The 18-pounder gun fell far behind 
all the rockets, a result, possibly, to be in part ascribed to 
the imperfection of the powder. The performance of the 
syren was, on the whole, less satisfactory than that of the 
rocket. The instrument was worked, not by steam of 70 
Ibs. pressure, as at the South Foreland, but by compressed 
air, beginning with 40 Ibs. and ending with 30 Ibs. 
pressure. The trumpet was pointed to windward, and 
in the axis of the instrument the sound was about as 
effective as that of the 8-oz. rocket. But in a direction at 
right angles to the axis, and still more in the rear of this 
direction, the syren fell very sensibly behind even the 2-oz. 
rocket. 
These are the principal comparative trials made between 
the gun-cotton rocket and other fog-signals; but they are 
not the only ones. On the 3d of August, 1877, for 
example, experiments were made at Lundy Island with the 
following results. At 2 miles distant from the firing-point, 
with land intervening, the 18-pounder, firing a 3-1 b. 
charge, was quite unheard. Both the 4-oz. rocket and the 
8-oz. rocket, however, reached an elevation which com- 
manded the acoustic shadow, and yielded loud reports. 
When both were in view the rockets were still superior to 
the gun. On the 6th of August, at St. Ann's, the 4-oz. 
and 8-oz. rockets proved superior to the syren. On the 
