Signalling and Safety at Sea. 3 



the thunder, the scene of the discharge must be about 1100 

 feet distant. If two seconds elapse the distance is 2200 

 feet, and so on. The whole theory of synchronous signalling 

 is involved in this time-honoured chapter of domestic science. 

 For suppose a gun to be fired from a lightship guarding 

 some peril of the coast, and simultaneously with the explosion 

 a light be flashed from the lantern of the lightship ; a vessel 

 afar off sees first the flash — at the very instant of its 

 occurrence— and later she receives the sound of the gun. 

 For every second of interval between the seeing of the flash 

 a.nd hearing of the gun about 1100 feet may be allowed. 

 If the interval w T as 3i seconds then the ship is 1100 x3| = 

 3850 feet distant from the lightship. But this is just the 

 information which the mariner approaching at night values 

 above all other and which is most conducive to his safety. 

 It gives him the means of determining not only his distance 

 from the danger guarded by the lightship but also it gives 

 him his actual position. 



On the existing system of coast signals the mariner is 

 given the light and the sound in no way co-ordinated one 

 with another. Each of these signals, therefore, is aimed 

 at accomplishing the same thing, i. e. telling the sailor the 

 direction in which the danger lies. They give him, also, 

 some idea of his distance as being within the limits of 

 visibility or audibility of the one or other of the signals. 

 But the inference of distance is so affected by weather con- 

 ditions as to be uncertain and even deceptive in character. 

 It is possible to hear the gun of the lightship and to think 

 it sometimes close by and again far off, and for the direction 

 of the sound to remain quite uncertain. The bearing of the 

 light is indeed certain when it is visible. Our coast signals, 

 as at present ordered, therefore, give the mariner at best the 

 bearing of the danger and but a rough and uncertain in- 

 dication of distance. But the synchronized signals we have 

 •described give him not only the bearing but a determination 

 of distance sufficiently accurate to enable him to fix his 

 position. 



In oider to understand this clearly let I (PL I. fig. 1) mark 

 the position of the lighthouse. The circle struck round it is 

 to the radius d, which is the distance as determined by the 

 synchronous signal. The ship must be located somewhere 

 on this circle. If now the bearing of / from the ship is 

 8.W., the ship is at x . It cannot be anywhere else. And 

 evidently the bearing of the light and the distance must, 

 similarly, in every case give the sailor his position. 



There are objections, as we have seen, to the use of sound 



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