RECENT EXPERIMENTS ON FOG-SIGNALS 275 



tion, it may be expected that they will also vary as pro- 

 ducers of sound. This theoretic inference is completely 

 verified by experiment. In a series of preliminary trials 

 conducted at Woolwich on the 4th of June, 1875, the 

 sound -producing powers of four different kinds of powder 

 were determined. In the order of the size of their grains 

 they bear the names respectively of Fine-grain (F. G.), 

 Large-grain (L. GK), Eifle Large-grain (E. L. G-.), and 

 Pebble-grain (P.) (See annexed figures.) The charge in 

 each case amounted to 4^ Ibs.; four 24-lb. howitzers 



P.G. L.G. 



being employed to fire the respective charges. There 

 were eleven observers, all of whom, without a single dis- 

 sentient, pronounced the sound of the fine -grain powder 

 loudest of all. In the opinion of seven of the eleven the 

 large-grain powder came next; seven also of the eleven 

 placed the rifle large-grain third on the list; while they 

 were again unanimous in pronouncing the pebble-powder 

 the worst sound -producer. These differences are entirely 

 due to differences in the rapidity of combustion. All who 

 have witnessed the performance of the 80-ton gun 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 



