1878.] Prof. Tyndail. Experiments on Fog-Signals. 253 



rockets were 12 oz., 8 oz., 4 oz., and 2 oz., of gun-cotton respectively. 

 The gun and the four rockets constituted a series, and eight; series were 

 fired during the afternoon of the 17th. The observations were made 

 from the " Vestal " and the " Gralatea," positions being assumed which 

 permitted the sound to reach the observers with the wind, against the 

 wind, and across the wind. The distance of the " Galatea " varied from 

 3 to 7 miles, that of the "Vestal," which was more restricted in her 

 movements, being 2 to 3 miles. Briefly summed up, the result is that 

 the howitzer, firing a 3-lb. charge, which it will be remembered was 

 our best gun at the South Foreland, was beaten by the 12-oz. rocket, 

 by the 8-oz. rocket, and by the 4-oz, rocket. The 2-oz. rocket alone 

 fell behind the howitzer. 



It is worth while recording the distances to which some of the 

 sounds were heard on the day now referred to : — 



1. Leigh 6| miles W.N.W. . . 24 out of 40 sounds heard. 



2. airdler Light-vessel . . 12 „ S.E. by B. . . 5 „ „ 



3. Eeculvers 17* „ S.E. by S. . . 18 „ „ 



4. St. Nicholas 20 „ S.E. 3 



5. Epple Bay .... , 22 „ S.E. by E. . . 19 



6. Westgate 23 „ S.E. by E... 9 



7. Kingsgate 25 „ S.E. by E. . . 8 



The day was cloudy, with occasional showers of drizzling rain ; the 

 wind about N.W. by JST. all day ; at times squally, rising to a force of 

 6 and 7 and sometimes dropping to a force of 2 or 3. The station at 

 Leigh excepted, all these places were to leeward of Shoeburyness. At 

 four other stations to leeward, varying in distance from 15J to 24J 

 miles, nothing was heard, while at eleven stations to windward, vary- 

 ing from 8 to 26 miles, the sounds were also inaudible. It was found, 

 indeed, that the sounds proceeding against the wind did not penetrate 

 much beyond 3 miles. 



On the following day, viz., the 18th October, we proceeded to Dunge- 

 ness with the view of making a series of strict comparative experi- 

 ments with gun-cotton and cotton-powder. Rockets containing 8 oz., 

 4oz., and 2 oz. of gun-cotton had been prepared at the Royal Arsenal ; 

 while others, containing a similar quantity 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 lbs. of powder. 



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 also illustrated in a very 

 striking manner, only a single unit separating the numerical value of 

 the 8-oz. rocket from that of the 2-oz. rocket. The former was re- 

 corded as 6*9 and the latter, as 5*9, the value of the 4-oz. charge being 

 intermediate between them. These results were recorded by a number 



s 2 



