Signalling and Safety at Sea. 11 



the distance at which the bell is heard depend on the bearing 

 or! the bell from the ship. If the bell is right aft no sound 

 is heard save at close quarters. In this case the stoppage 

 of the sound is assisted by the action of the propellers in 

 breaking up the medium. A bearing right abeam is^, 

 generally, the best. The sounds weaken when well forward. 

 Sounds coming from the opposite side of the vessel are not 

 heard save at small distances from the bell. 



While weather conditions affect to some extent the picking 

 up of the signals — chiefly ow T ing to noises developed by the 

 pitching of the vessel — the signals are recognizable at long 

 distances in an}' w T eather. 



it is evident that o£ all modes of synchronous signalling 

 which may be suggested, the combination of under-water 

 sounds and wireless dot is the most free from liability to 

 failure. True the sensitiveness is not so great as we obtain 

 by other combinations. Bat facilities for receiving such 

 signals are confined — it may be said — to the larger vessels, 

 and these approach at such speeds that they obtain all they 

 require if they can determine their distance from the shore 

 to an accuracy of one quarter of a mile or even of half a mile. 

 They should be able to effect the more accurate determination 

 by this combination. If the radio dot is sent out at intervals 

 of about 0*6 second the submarine bell-stroke lags the 

 interval between two dots for each half sea-mile traversed. 

 If the ship is 5 miles off the coast the sound lags 10 such 

 intervals, and the bell comes in with the 10th dot, supposing 

 that the first dot is emitted 0*6 second later than the first 

 bell-stroke. In this case the sailor counts up the dots, and 

 so obtains the number. of half sea-miles separating his ship 

 from the signal station. As it is quite possible to tell when 

 the bell-stroke falls somewhere between two consecutive 

 radio dots, estimation to the J sea-mile is feasible. 



In these operations the receipt of the signals is effected by 

 listening with one ear to the bell sounds and with the other 

 to the radio sounds, — a telephone receiver covering each ear 

 of the operator. 



In September 1911, the United States Hydrographic 

 Department undertook an experiment on the use of 

 synchronized signals in air, water, and aether. The signals 

 were sent out from the Nantucket Lightship near New T York 

 (see fig. 3, PL I.). The aerial sound signals were created by 

 blast from a steam whistle and those in water by submarine 

 bell. At the instant the whistle blew, a wireless tick of two 

 or three seconds' duration was sent out, and simultaneously 

 with the making of the contact the valve of the striking 



