248 Prof. Tyndall. Experiments on Fog-Signah. [Mar. 21, 



most cases have incurred the labour of reducing and reporting on 

 the observations. Guns of various forms and sizes have been invoked 

 for gunpowder, while gun-cotton has been fired in free air, and in the 

 foci of parabolic reflectors. 



On the 22nd of February, 1875, a number of small guns, cast 

 specially for the purpose — some with plain, some with conical, and 

 some with parabolic muzzles, firing 4 oz. of fine-grain powder, were 

 pitted against 4 oz. of gun-cotton, detonated both in the open and in 

 the focus of a parabolic reflector.* The sound produced by the gun- 

 cotton, reinforced by the reflector, was unanimously pronounced 

 loudest of all. With equal unanimity, the gun-cotton detonated in 

 free air was placed second in intensity. Though the same charge 

 was used throughout, the guns differed notably among themselves, 

 but none of them came up to the gun-cotton, either with or without 

 the reflector. A second series, observed from a different distance on 

 the same day, confirmed to the letter the foregoing result. 



As a practical point, however, the comparative cost of gun cotton 

 and gunpowder has to be taken into account, though considerations 

 of cost ought not to be stretched too far in cases involving the 

 safety of human life. In the earlier experiments, where quantities 

 of equal price were pitted against each other, the results were 

 somewhat fluctuating. Indeed, the perfect manipulation of the gun- 

 cotton required some preliminary discipline — promptness, certainty, 

 and effectiveness of firing, augmenting as experience increased. 

 As lib. of gun-cotton costs as much as 3 lbs. of gunpowder, these 

 quantities were compared together on the 22nd of February. The 

 guns employed to discharge the gunpowder were a 12-lb. brass 

 howitzer, a 24-lb. cast-iron howitzer, and the long 18-pounder used 

 at the South Foreland. The result recorded is, that the 24-lb. 

 howitzer, firing 3 lbs. of gunpowder, had a slight advantage over 1 lb. 

 of gun-cotton detonated in the open; while the 12=lb. howitzer and 

 the 18-pounder were both beaten by the gun-cotton. On the 2nd of 

 May, on the other hand, the gun-cotton is reported as having been 

 beaten by all the guns. 



Meanwhile, the parabolic muzzle-gun, expressly intended for fog- 

 signalling, was pushed rapidly forward, and on the 22nd and 23rd of 

 March, 1876, its power was tested at Shoeburyness. Pitted against it 

 were a 16-pounder, a 5 J- inch howitzer, 1^ lb. of gun-cotton detonated 

 in the focus of a reflector, and 1^ lb. of gun-cotton detonated in free air. 

 On this occasion, nineteen different series of experiments were made, 

 when the new experimental gun, firing a 3-lb. charge, demonstrated 

 its superiority over all guns previously employed to fire the same 

 charge. As regards the comparative merits of the gun-cotton fired in 



* For charges of this weight the reflector is of moderate size, and may be em- 

 ployed without fear of fracture. 



