1889.] on Beacon Lir/hfs and For/ Sh/uaJ^. 443 



known scientific and practical results obtained, togetlier with the 

 ascertained relative merits of sound-producing instruments for tha 

 service of the mariner, have proved to be of the highest scientific 

 interest and practical importance. The investigation at the South 

 Foreland was followed up by the Trinity House with further explosivv'? 

 fog signal experiments, in which they were assisted by the authori- 

 ties at Woolwich Arsenal, with guns of various forms, weight of 

 charges, and descriptions of gunpowder. The powders tested were 

 — (1) fine grain, (2) larger grain, (3) rifle large grain, and (4) 

 pebble. The result placed the sound-producing powers of these 

 powders exactly in the order above stated ; the fine grain, or most 

 rapidly burning powder, gave indisputably the loudest sound, while 

 the report of the slowly burning pebble powder, was weakest of all. 

 Here, again, the greater value of increased rapidity of combustion in 

 producing sound, was demonstrated. It was found that charges of 

 gun-cotton yielded reports louder at all ranges than equal chargew 

 of the best gunpowder ; and further experiments proved the ex- 

 plosion of half-a-pound of gun-cotton gave a sound equal in 

 intensity to that, produced by three pounds of the best gunpowder. 

 These ijivestigations led the Trinity House to adopt gun-cotton for 

 fog signals at isolated stations on rocks and shoals, as already 

 described, where, from want of space, it had hitherto been possible 

 to apply nothing better than a bell, or gong. Of all the sound 

 signals now employed, for the warning and guidance of mariners 

 during fog, viz. bells, gongs, guns, whistles, reed trumpets, sirens, 

 and sounds produced by the explosion of gun-cotton, the blasts 

 of the siren, and explosions of gun-cotton, have been found to 

 be the most efficient for coast fog signals ; therefore these signals 

 have received the greatest care and attention in their development. 

 The siren doubtless ranks first, for stations wherever it can be 

 applied, chiefly on account of its economy in maintenance, and the 

 facility it affords for giving prolonged blasts of any desired intensity 

 or pitch, and thus providing any number of trustworthy distinctive 

 characters that may be required to ensure individuality in the signal. 

 Sirens are now employed at many floating and shore stations of the 

 Trinity House, and one recently installed at Saint Catherine's Light- 

 house, Isle of Wight, of the automatic Holmes type, of which we have 

 here a model, absorbs during its blast not less than 600 horse-jDOwer. 

 The audibility of the blasts of this instrument may be considered to 

 be trustworthy at a range of two miles under all conditions of foggy 

 atmosphere on the sea surface over which it is intended to be sounded. 

 It is very desirable that for many landport stations a greater trust- 

 worthy range be provided for the mariner, but this can only be 

 afforded by such increased power as would be required for a more 

 powerful electric light installation to serve the mariner in other 

 gradations of thick atmosphere. A very important improvement 

 and economy have lately been effected in the sirens of the Trinity 

 House by rendering them always instantaneously available for 

 Vol. XIT. (No.'.S3.) 2 h 



