RECENT EXPERIMENTS ON FOG-SIGNALS. 271 



24 out of 40 sounds heard. 



The day was cloudy, with occasional showers of 

 drizzling rain ; the wind about N.W. by N. all day ; at 

 times squally, rising to a force of 6 or 7 and sometimes 

 dropping to a force of 2 or 3. The station at Leigh 

 excepted, all these places were to leeward of Shoebury. 

 ness. At four other stations to leeward, varying in 

 distance from 15 J to 24^ miles, nothing was heard, 

 while at eleven stations to windward, varying from 8 to 

 26 miles, the sounds were also inaudible. It was found, 

 indeed, that the sounds proceeding directly against the 

 wind did not penetrate much beyond 3 miles. 



On the following day, viz. the 1 8th October, we 

 proceeded to Dungeness with the view of making a 

 series of strict comparative experiments with gun-cotton 

 and cotton-powder. Eockets containing 8 oz., 4 oz., 

 and 2 oz. of gun-cotton had been prepared at the Koyal 

 Arsenal ; while others, containing similar quantities of 

 cotton-powder, had been supplied by the Cotton-powder 

 Company at Faversham. With these were compared 

 the ordinary 18-pounder gun, which happened to be 

 mounted at Dungeness, firing the usual charge of 3 Ibs. 

 of powder, and a syren. 



From these experiments it appeared that the gun- 

 cotton and cotton-powder were practically equal as 

 producers of sound. 



The effectiveness of small charges was illustrated in 

 a very striking manner, only a single unit separating 

 the numerical value of the 8-oz. rocket from that of tha 



