RECENT EXPERIMENTS ON FOG-SIGNALS. 267 



or it may be twenty, miles before she reached the rock 

 which wrecked her. Had the fleet possessed such a 

 signal, instead of the ubiquitous but ineffectual whis- 

 tle, the ' Iron Duke ' and * Vanguard ' need never have 

 come into collision. 



It was the necessity of providing a suitable signal 

 for rock lighthouses, and of clearing obstacles which 

 cast an acoustic shadow, that suggested the idea of the 

 gun-cotton rocket to Sir Richard Collinson, Deputy 

 Master of the Trinity House. His idea was to place a 

 disk or short cylinder of gun-cotton in the head of a 

 rocket, the ascensional force of which should be em- 

 ployed to carry the disk to an elevation of 1,000 feet or 

 thereabouts, where by the ignition of a fuse associated 

 with a detonator, the gun-cotton should be fired, send- 

 ing its sound in all directions vertically and obliquely 

 down upon earth and sea. The first attempt to realise 

 this idea was made on July 18, 1876, at the firework 

 manufactory of the Messrs. Brock, at Nunhead. Eight 

 rockets were then fired, four being charged with 5 oz. 

 and four with 7 oz. of gun-cotton. They ascended to 

 a great height, and exploded with a very loud report in 

 the air. On July 27, the rockets were tried at Shoe- 

 buryness. The most noteworthy result on this occa- 

 sion was the hearing of the sounds at the Mouse Light- 

 house, 8 miles E. by S., and at the Chapman Light- 

 house, 8 miles W. .by N.; that is to say, at opposite 

 sides of the firing-point. It is worthy of remark that, 

 in the case of the Chapman Lighthouse, land and trees 

 intervened between the firing-point and the place of 

 observation. ' This,' as General Younghusband justly 

 remarked at the time, * may prove to be a valuable con- 

 sideration if it should be found necessary to place a 

 signal station in a position whence the sea could not 

 be freely observed.' Indeed, the clearing of such ob- 



