276 FRAGMENTS OF SCIENCE 



tube of the gun these lumps of solid matter gradually re- 

 solve themselves into gas, which on issuing from the muz- 

 zle 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 condensation to rarefaction with a ra- 

 pidity sufficient to forestall the formation of the wave. On 

 d priori grounds, then, we are entitled to infer the effective- 

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

 experiments, stretching from 1874 to the present time, this 

 inference has been verified in the most conclusive manner. 



As regards explosive material, and zealous and accom- 

 plished help in the use of it, the resources of Woolwich 

 Arsenal have been freely placed at the disposal of the 

 Elder Brethren. General Campbell, General Younghus- 

 band, Colonel Fraser, Colonel Maitland, and other officers, 

 have taken an active personal part in the investigation, 

 and in most cases have incurred the labor 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 22d 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 



