RECENT EXPEKIMENTS ON FOG-SIGNALS. 269 



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 silence 

 after seven seconds' duration. These echoes were of 

 the same character as those so frequently noticed 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 obser- 

 vations being that the sounds were heard at Tillingham, 

 10 miles to the N.E. ; at West Mersea, 15| miles to the 

 N.E. by E. ; at Brightlingsea, 17J miles to the N.E. ; 

 and at Clacton Wash, 20J 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- 

 Ib. 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 explo- 

 sive material being thus compressed into the same 

 volume, Mr. Gardiner thought that a greater sonorous 

 eiFect 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 Faversharn, on the 1 6th of 

 June, 1877. The weights of cotton-powder employed 

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

 and of signals fired a few feet above the ground. The 

 experiments throughout were arranged and conducted 

 by Mr. Mackie. Our desire on this occasion was to get 

 as near to windward as possible, but the Swale and 



