IMrUOVKMKNTS IN COAST r<IGNAI..S. "iSQ 



the intensity in its blasts conaparcd with that of a similar apparatus if 

 sounded continuously. This matter of accnmulativo intensity is a con- 

 sideration of very great importance in determining the periods of a siren 

 fog signal in relation to its efficiency for the service of the mariner. 



It is evident that, if wo adopt a '2 minutes' period for siren coast 

 signal blasts, the number of distinctive characters would be limited to 

 about iive, viz. : — 



One blast every 2 minutes. 



"I'wo „ „ 



Three „ „ „ 



Four „ „ 



Five „ ., „ 



If, for the purpose of extending the above code, short and long blasts 

 be adopted, a serious loss of power must be incurred with the long blasts ; 

 further, it is found to be very desirable to diffei-entiate the sounds of 

 coast sound signals as completely as possible from the sounds of the 

 whistles and horn signals of steam and sailing vessels ; therefore, the 

 question of establishing a code of siren coast blasts composed of notes of 

 high and low pitch has lately received the careful consideration of the 

 Trinity House, and, so far, promises to be very successful. The system 

 has the advantage of the same alphabetical letter or number being appro- 

 priated to the light and the f^ound signal at each station, which is found 

 to be advantageous in aiding the memory of the mariner. I have shown 

 on the previous page a complete alphabetical code of distinctive charactors 

 for coast signals, which can thus be adopted, each signal being composed 

 of a combination of high and low notes. The signals A, G, K, N, R, and 

 U have been already adopted by the Trinity Ifouse. After a series of 

 cxhaustiv^e experimental trials, a high note of G70 vibrations per second 

 and alow note of 290 vibrations per second have been adopted. A slight 

 inferiority in the audibility of the high note, as compared with that of the 

 low note, is found to exist whcro tliey botli start with the same initial 

 power ; but this defect is remedied by increasing the area of the ports 

 of the high-note siren abont 20 per cent. On Plate IV. is shown one 

 of the most recent cylindrical tirst-class sirens in the service of the 

 Trinity House for sounding a liigli and a low note. Tlie walls of the 

 cylindrical siren chamber, and the corresponding chamber in wliich it 

 revolves, have two oblique rows of ports, one above the other. The lower 

 row, for the low iiote, contains fourteen ports, and the upper row, for 

 the high note, contains thirty-two ports. ' The siren is surrounded by an 

 .annular chamber which is divided by a horizontal partition, so that the 

 compressed air or steam for sounding the instrument can be admitted 

 separately to the high or low note ports. On the spindle of the siren, at 

 the lower part, is fitted a centrifugal governor, which is readily adjustable 

 for any required speed of the insti'ument. It will thus be seen that, by 

 any simple automatic arrangement for the admission of compressed air or 

 steam to the upper or lower ports, any desired distinctive character can 

 be given to the signal.' 



' To Mr. G. II. Slight, yupoiintondoiit o£ the Trinity House W()ri<shops, is due the 

 cylindrical form of the instrument, and the adjustable (ieiitrifugal governor by whioli 

 the speed is controlled. The improvi'inent of the instrument in rciiderin,^ it, auto- 

 in.'itic in its action, instead of l)ein<j driven by a belt and pulley, was patented in 

 1875 by Ilalmes, the inventor ol' the first nuignoto-clectric machine adopted for 

 lighthouses. 



