Page:Popular Science Monthly Volume 13.djvu/297

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RECENT EXPERIMENTS ON FOG-SIGNALS.

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 previously with the Deputy Master of the Trinity House and myself, a committee 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 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 limited our distance to 112 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 "aërial echoes," which invariably followed the explosion of the rockets, were loud and long continued, shading off, as in all previous cases, by imperceptible gradations, 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 rockets 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 observations 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 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-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. Leigh 612 miles west-northwest 24 out of 40 sounds heard.
2. Girdler Light-vessel 12 " southeast by east 5 ""
3. Reculvers 1712 " 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 ""
7. Kingsgate 25 " southeast by east 8 ""