RECENT EXPERIMENTS ON FOG-SIGNALS. 265 



to the wire this never occurred. To the circumstance 

 that the broadsides of the slabs faced the sea is prob- 

 ably to be ascribed the remarkable fact observed on 

 March 23, that in two directions, not far removed from 

 the line of fire, the gun-cotton detonated in the open 

 had a slight advantage over the new gun. 



Theoretic considerations rendered it probable that 

 the shape and size of the exploding mass would affect 

 the constitution of the wave of sound. I did not think 

 large rectangular slabs the most favourable shape, and 

 accordingly proposed cutting a large slab into frag- 

 ments of different sizes, and pitting them against each 

 other. The differences between the sounds were by no 

 means so great as the differences in the quantities of 

 explosive material might lead one to expect. The 

 mean values of eighteen series of observations made on 

 board the ' Galatea,' at distances varying from If mile 

 to 4.8 miles, were as follows: 



Weights . . 4 oz. 6 oz. 9 oz. 12 oz. 

 Value of sound . 3.12 3.34 4.0 4.03 



These charges were cut from a slab of dry gun- 

 cotton about If inch thick: they were squares and rec- 

 tangles of the following dimensions: 4 oz., 2 inches 

 by 2 inches; 6 oz., 2 inches by 3 inches; 9 oz., 3 inches 

 by 3 inches; 12 oz., 2 inches by 6 inches. 



The numbers under the respective weights express 

 the recorded value of the sounds. They must be sim- 

 ply taken as a ready means of expressing the approxi- 

 mate relative intensity of the sounds as estimated by 

 the ear. When we find a 9-oz. charge marked 4, and a 

 12-oz. charge marked 4.03, the two sounds may be re- 

 garded as practically equal in intensity, thus proving 

 that an addition of 30 per cent, in the larger charges 

 produces no sensible difference in the sound. Were 



