RECENT EXPERIMENTS ON FOG SIGNALS. 205 
house, land and trees intervened between the firing-point 
and the place of observation. " This/' as General Young- 
husband 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 eleva- 
tion 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, how- 
ever, 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 oz. On Thursday, March 8, 1877, 
these comparative experiments of firing at high and low 
elevations were pushed still further. The gun-cotton near 
the ground consisted of |-lb. disks, suspended from a hor- 
izontal iron bar about 4 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 direc- 
tion 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 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. 
Toward 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 ab- 
solutely 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 soli4 
