268 FRAGMENTS OF SCIENCE. 



stacks was one of the objects which the inventor of the 

 rocket had in view. 



With reference to the action of the wind, it Avas 

 thought desirable to compare the range of explosions 

 produced near the surface of the earth with others 

 produced at the elevation 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, however, 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, sus- 

 pended from a horizontal 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 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 ex- 

 plosions near the ground by a small but sensible quan- 

 tity. 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 re- 

 maining five the rocket had the advantage. 



Towards the close of the day the atmosphere be- 

 came very serene. A few distant cumuli sailed near 



