2 8o THE POPULAR SCIENCE MONTHLY. 



play. But the reenforcement of the sound in one direction implies its 

 withdrawal from some other direction, and accordingly it was found that 

 at a distance of h\ miles from the firing-point, and on a line including 

 nearly an angle of 90 with the line of fire, the gun-cotton in the open 

 beat the new gun ; while behind the station, at distances of 8 miles 

 and 13-J miles respectively, the gun-cotton in the open beat both the gun 

 and the gun-cotton in the reflector. This result is rendered more im- 

 portant by the fact that the sound reached the Mucking Light, a dis- 

 tance of 13^ miles, against a light wind which was blowing at the time. 



Most, if not all, of our ordinary sound-producers send forth waves 

 which are not of uniform intensity throughout. A trumpet is loudest 

 in the direction of its axis. The same is true of a gun. A bell, with 

 its mouth pointed upward or downward, sends forth waves far denser in 

 the horizontal plane passing through the bell than at an angular dis- 

 tance of 90 from that plane. The oldest bell-hangers must have been 

 aware of the fact that the sides of the bell, and not its mouth, emitted 

 the strongest sound, their practice being determined by this knowledge. 

 Our slabs of gun-cotton also emit waves of different densities in differ- 

 ent parts. It has occurred in the experiments at Shoeburyness that 

 when the broad side of a slab was turned toward the suspending wire of 

 a second slab six feet distant, the wire was cut by the explosion, while, 

 when the edge of the slab was turned to the wire, this never occurred. 

 To the circumstance that the broad sides of the slabs faced the sea is 

 probably to be ascribed the remarkable fact observed on the 23d of March, 

 that in two directions, not far removed from the line of fire, the gun-cot- 

 ton 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 favorable shape, and 

 accordingly proposed cutting a large slab into fragments 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 quanti- 

 ties of explosive material might lead one to expect. The mean values 

 of eighteen series of observations made on board the Galatea, at dis- 

 tances varying from If mile to 4.8 miles, were as follows : 



Weights 4-ounce 6-ounce 9-ounce 12-ounce V-ounce rocket. 



Value of sound 3.12 3.34 4.0 4.03 3.35 



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 ounces, 2 inches by 2 inches ; 6 ounces, 2 inches by 3 inches ; 9 ounces, 

 3 inches by 3 inches ; 12 ounces, 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 ex- 

 pressing the approximate relative intensity of the sounds as estimated 

 by the ear. When we find a 9-ounce charge marked 4, and a 12-ounce 

 charge marked 4.03, the two sounds may be regarded as practically equal 



