RECENT EXPERIMENTS ON FOG-SIGNALS. 209 



the horizon, but the zenith and a vast angular space all 

 round it were absolutely 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 solid nucleus of sound was a 

 continuous train of echoes, which retreated to a con- 

 tinually greater distance, dying gradually off into si- 

 lence after seven seconds' duration. These echoes 

 were of the same character as those so frequently no- 

 ticed at the South Foreland in 1872-73, and called by 

 me ' aerial echoes/ 



On the 23rd of March the experiments were re- 

 sumed, the most noteworthy results of that day's ob- 

 servations being that the sounds were heard at Tilling- 

 ham, 10 miles to the N.E.; at West Mersea, lof 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. howitzer, 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 in- 

 stance of Mr. Mackie, who had previously gone very 

 thoroughly into the subject, a Committee 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 em- 

 ployed were 2 oz., 8 oz., 1 lb., and 2 Ibs., in the form of 



