266 FRAGMENTS OF SCIENCE. 



the sounds estimated by some physical means, instead 

 of by the ear, the values of the sounds at the distances 

 recorded would not, in my opinion, show a greater 

 advance with the increase of material than that indi- 

 cated by the foregoing numbers. Subsequent experi- 

 ments rendered still more certain the effectiveness, 

 as well as the economy, of the smaller charges of gun- 

 cotton. 



It is an obvious corollary from the foregoing ex- 

 periments that on our ' nesses ' and promontories, 

 where the land is clasped on both sides for a consider- 

 able distance by the sea where, therefore, the sound 

 has to propagate itself rearward as well as forward 

 the use of the parabolic gun, or of the parabolic re- 

 flector, might be a disadvantage rather than an advan- 

 tage. Here gun-cotton, exploded in the open, forms 

 the most appropriate source of sound. This remark 

 is especially applicable to such lightships as are in- 

 tended to spread the sound all round them as from cen- 

 tral foci. As a signal in rock lighthouses, where nei- 

 ther syren, steam-whistle, nor gun could be mounted; 

 and as a handy fleet-signal, dispensing with the lumber 

 of special signal-guns, the gun-cotton will prove in- 

 valuable. But in most of these cases we have the 

 drawback that local damage may be done by the ex- 

 plosion. The lantern of the rock lighthouse might 

 suffer from concussion near at hand, and though me- 

 chanical arrangements might be devised, both in the 

 case of the lighthouse and of the ship's deck, to place 

 the firing-point of the gun-cotton at a safe distance, 

 no such arrangement could compete, as regards sim- 

 plicity and effectiveness, with the expedient of a gun- 

 cotton rocket. Had such a means of signalling existed 

 at the Bishop's Rock lighthouse, the ill-fated 'Schiller' 

 might have been warned of her approach to danger ten, 



