RECENT EXPERIMENTS ON FOG SIGNALS. 203 



shape and size of the exploding mass would affect the con- 

 stitution of the wave of sound. I did not think large rec- 

 tangular slabs the most favorable shape, and accordingly 

 proposed cutting a large slab into fragments of different 

 sizes, and pitting them against each other. The dif- 

 ferences 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 rectangles 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 simply taken 

 as a ready means of expressing the approximate 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 regarded as practically equal 

 in intensity, thus proving that an addition of 30 percent, 

 in the larger charges produces no sensible difference in the 

 sound. Were the sounds estimated by some physical 

 means, instead of by the ear, the values of the sounds at 

 the distances recorded would not, in my opinion, show a 

 greater advance with the increase of material than that 

 indicated by the foregoing numbers. Subsequent experi- 

 ments rendered still more certain the effectiveness, as well 

 as the economy, of the smaller charges of gun-cotton. 



It is an obvious corollary from the foregoing experiments 

 that on our " nesses" and promontories, where the land is 

 clasped on both sides for a considerable distance by the 

 sea where, therefore, the sound has to propagate itself 

 rearward as well as forward the use of the parabolic gun, 

 or of the parabolic reflector, might be a disadvantage 

 rather than an advantage. Here gun-cotton, exploded in 

 the open, forms the most appropriate source of sound. 

 This remark is especially applicable to such lightships as 



