278 THE POPULAR SCIENCE MONTHLY. 



are entirely due to differences in the rapidity of combustion. All who 

 have witnessed the performance of the 80-ton gun at Woolwich must 

 have been surprised at the mildness of its thunder. To avoid the strain 

 resulting from quick combustion, the powder employed is composed of 

 lumps far larger than those of the pebble-powder above referred to. In 

 the long tube of the gun these lumps of solid matter gradually resolve 

 themselves into gas, which on issuing from the muzzle imparts a kind 

 of push to the air, instead of the sharp shock necessary to form the 

 condensation of an intensely sonorous wave. 



These are some of the physical reasons why gun-cotton might be 

 regarded as a promising fog-signal. Firing it as we have been taught 

 to do by Mr. Abel, its explosion is more rapid than that of gunpowder. 

 In its case the air-particles, alert as they are, will not, it might be 

 presumed, be able to slip from places of condensation to places of rare- 

 faction with a rapidity sufficient to forestall the formation of the wave. 

 On a priori grounds, then, we are entitled to infer the effectiveness of 

 gun-cotton, while in a great number of comparative experiments, 

 stretching from 1874 to the present time, this inference has been veri- 

 fied in the most conclusive manner. 



On the 22d of February, 1875, a number of small guns, cast special- 

 ly for the purpose some with plain, some with conical, and some with 

 parabolic muzzles, firing 4 ounces of fine-grain powder were pitted 

 against 4 ounces of gun-cotton, detonated both in the open and in 

 the focus of a parabolic reflector. 1 The sound produced by the gun- 

 cotton, reenforced by the reflector, was unanimously pronounced loud- 

 est 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 not 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 fluctu- 

 ating. Indeed, the perfect manipulation of the gun-cotton required 

 some preliminary discipline promptness, certainty, and effectiveness 

 of firing, augmenting as experience increased. As 1 pound of gun- 

 cotton costs as much as 3 pounds of gunpowder, these quantities were 

 compared together on the 22d of February. The guns employed to 

 discharge the gunpowder were a 12-pound brass howitzer, a 24-pound 

 cast-iron howitzer, and the long 18-pounder used at the South Foreland. 

 The result recorded is, that the 24-pound howitzer, firing 3 pounds of 



1 For charges of this weight the reflector is of moderate size, and may be employed 

 without fear of fracture. 



