RECENT EXPERIMENTS ON FOG-SIGNALS. 283 



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 been in communication pre- 

 viously with the Deputy Master of the Trinity House and myself, a 

 committee of the Elder Brethren visited the cotton-powder manufac- 

 tory, on the banks of the Swale, near Faversham, on the 16th of June, 

 1877. The weights of cotton-powder employed were 2 ounces, 8 ounces, 

 1 pound, and 2 pounds, 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 lim- 

 ited our distance to 1^ mile. We stood here east-southeast from the 

 firing-point, while the wind blew fresh from the northeast. 



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. The loudness of the sound was by no means 

 proportional to the quantity of the material exploded, 8 ounces yielding 

 very nearly as loud a report as 1 pound. The "aerial echoes," which 

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

 continued, shading off, as in all previous cases, by imperceptible grada- 

 tions, into silence. 



On the 17th of October, 1877, another series of experiments with 

 howitzers and rockets was carried out at Shoeburyness. The charge of 

 the howitzer was 3 pounds of L. G. powder. The charges of the rock- 

 ets were 12 ounces, 8 ounces, 4 ounces, and 2 ounces, 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 observa- 

 tions were made from the Vestal and the Galatea, 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 Ga- 

 latea varied from 3 to 7 miles, that of the Vestal, which was more re- 

 stricted in her movements, being 2 to 3 miles. Briefly summed up, 

 the result is that the howitzer, firing a 3-pound charge, which it will be 

 remembered was our best gun at the South Foreland, was beaten by the 

 12-ounce rocket, by the 8-ounce rocket, and by the 4-ounce rocket. The 

 2-ounce 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. Lei^h 6 miles west-northwest 24 out of 40 sounds heard. 



2. Girdler Light-vessel.. .12 " southeast by east. . 5 



3. Reculvers 11 % " southeast by south.. 18 



4. St. Nicholas 20 " southeast 3 



5. Epple Bay 22 " southeast by east. . 19 



6. Westgate 23 " southeast by east. . 9 



1. Kino-sgate 25 " southeast by east. . 8 



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