RECENT EXPERIMENTS ON FOG-SIGNALS 271 



of employing sound-signals in dense fogs. Bells, gongs, 

 horns, whistles, guns, and syrens have been used for this 

 purpose; but it is mainly, if not wholly, with explosive 

 signals that we have now to deal. The gun has been em- 

 ployed with useful effect at the North Stack, near Holy- 

 head, on the Kish Bank near Dublin, at Lundy Island, 

 and at other points on our coasts. During the long, labo- 

 rious, and I venture to think memorable, series of observa- 

 tions conducted under the auspices of the Elder Brethren 

 of the Trinity House at the South Foreland in 1872 and 

 1873, it was proved that a short 5>^-inch howitzer, firing 

 3 lbs. of powder, yielded a louder report than a long 

 18-pounder firing the same charge. Here was a hint to be 

 acted on by the Elder Brethren. The effectiveness of the 

 sound depended on the shape of the gun, and as it could 

 not be assumed that in the howitzer we had hit accident- 

 ally upon the best possible shape, arrangements were made 

 with the War Office for the construction of a gun specially 

 calculated to produce the loudest sound attainable from 

 the combustion of 3 lbs. of powder. To prevent the un- 

 necessary landward waste of the sound, the gun was fur- 

 nished with a parabolic muzzle, intended to project the 

 sound over the sea, where it was most needed. The con- 

 struction of this gun was based on a searching series of 

 experiments executed at Woolwich with small models, pro- 

 vided with muzzles of various kinds. A drawing of the 

 gun is annexed (p. 272). It was constructed on the prin- 

 ciple of the revolver, its various chambers being loaded 

 and brought in rapid succession into the firing position. 

 The performance of the gun proved the correctness of the 

 principles on which its construction was hased. 



An incidental point of some interest was decided by 



