IMPROVEMENTS IN COAST SIGNALS. 589 



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

 sounded continuously. This matter of accumulative 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 we adopt a 2 minutes' period for siren coast 

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

 about five, viz. : — 



One blast every 2 minutes. 



Two 



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 differentiate 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 sound 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 characters 

 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, B, and 

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

 exhaustive experimental trials, a high note of 670 vibrations per second 

 and a low 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 where they both start with the same initial 

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

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

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

 Trinity House for sounding a high and a low note. The walls of the 

 cylindrical siren chamber, and the corresponding chamber in which it 

 revolves, have two oblique rows of j)orts, one above the other. The lower 

 row, for the low note, 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 instrument. 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. 1 



1 To Mr. G. H. Slight, Superintendent of the Trinity House workshops, is due the 

 cylindrical form of the instrument, and the adjustable centrifugal governor by which 

 the speed is controlled. The improvement of the instrument in rendering it auto- 

 matic in its action, instead of being driven by a belt and pulley, was patented in 

 1875 by Holmes, the inventor of the first magneto-electric machine adopted for 

 lighthouses. 



