RKCENT 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-J 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 -J-lb. disks, suspended from a hor- 

 izontal iron bar about 4rj 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 groat elevation, 

 and exploded with a loud report. Following this solid 



