206 FRAGMENTS OF SCIENCE. 



nucleus of sound was a continuous train of echoes, which 

 retreated to a continually greater distanc e, 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 ine 

 " aerial echoes." 



On the 23d of March the experiments were resumed, 

 the most noteworthy results of that day's observations 

 being that the sounds were heard at Tillingham, 10 miles 

 to the N. E. ; at West Mersea, 15f 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 i 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. how- 

 itzer, 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 instance of Mr. Mackie, who had 

 previously gone very thoroughly into the subject, a com- 

 mittee 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 

 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 other 

 obstacles limited our distance to 1^ mile. We stood here 

 E. S. E. from the firing-point while the wind blew fresh 

 from the N. E. 



The cotton-powder yielded a very effective report. The 

 rockets in general had a slight advantage over the same 

 quantities of material fired near the ground. Theloudness 

 of the sound was by no means proportional to the quantity 

 of the material exploded, 8 oz. yielding very nearly as loud 

 a report as 1 lb. The "aerial echoes,'*' which invariably 

 followed the explosion of the rockets, were loud and long- 

 continued. 



