1870.] Proceedings of the Asiatic Society. 247 



present evidence goes, the beating of the surf seems a probable 

 cause, and it is the only definite cause that has been assigned. 



Mr. Westland said — " I hardly venture to differ in opinion with 

 Mr. Blanford on a matter of this nature, but it seems to me that 

 there is one very great difficulty in accepting the surf theory, which 

 I shall try to explain. 



In the first place, it must be remembered that these sounds are 

 heard some forty or fifty miles from the sea shore. This is a dis- 

 tance over which the sound of cannon even rarely travels so as to 

 be distinctly perceived, and even in the case of accumulated dis- 

 charges of cannon, such as in firing salutes, or in the case of a 

 battle, the instances of their being heard over such long distances, 

 are sufficiently rare to be regarded as unusual phenomena. Now in 

 the case of these "Barisal Guns" the noises are heard not rarely, 

 but frequently, over these long distances, and after forty or fifty 

 miles travelling from the sea, if they really come thence, they are 

 still sharp and well-heard sounds. If they are produced by the 

 breaking of surf, it is clear that to produce a sound loud enough 

 to be heard so well over such a long distance, it will require, not 

 the breaking of a wave at any one point, but the breaking of waves 

 over a considerable extent of shore. 



It is possible to imagine a wave breaking simultaneously over a 

 long line of shore, but unfortunately sound does not travel simul- 

 taneously. The travelling of sound is very slow indeed over such 

 a long distance as forty miles, and the concussion produced by the 

 breaking of one part of the wave would necessarily reach the obser- 

 ver's ear long before that produced by the breaking of another part ; 

 the sound of this simultaneously breaking wave would, to the distant 

 hearer, be scattered over a little space of time, and be therefore im- 

 perceptible through its being so scattered. The sound as it is 

 actually heard, however, is sufficiently sharp to be compared, as 

 it is by every one, with that of a gun. 



It is not therefore by a simultaneously breaking wave, that the 

 sound can be produced, but it can only be (on the wave-breaking 

 hypothesis) by a number of waves, or what is the same thing, 

 different parts of the same wave, breaking at different parts of the 

 coast, their moments of breaking being so arranged, that the sound 

 starting at these different moments from these differently distant 



