34 Prof. J. Joly on Scientific 



alteration of bearing there must be safety. The question is : 

 can it always be reliably employed ? It is a fact that just 

 when the courses of the vessels are so directed as to cause 

 the ships to rapidly approach one another, there may be 

 only a small change of bearing in a given time ; and for 

 the sailor to spend valuable minutes in setting the wireless 

 compass to the loudest sound in the telephone when the 

 ships are rapidly approximating one towards the other, 

 and when it is not known for certain whether 10 miles 

 or 3 miles separate them, is not a safe procedure. The 

 complete and final solution of the problem of collision 

 would appear to involve the determination of the distance 

 separating the vessels. Otherwise the navigator must make 

 his observations under conditions of anxiety ; and in the fear 

 lest worse should happen must frequently be driven to alter 

 needlessly the course of his ship. 



The 4th criterion — that foretelling collision by constancy in 

 the rate of approach, as in the case of the method by constancy 

 of bearings, does not involve knowledge of courses and speeds. 

 But it possesses the very great advantage of keeping the 

 sailor informed all the time of the distance separating the 

 vessels ; obviously an important element of safety and 

 conducive to the peace of mind of all concerned. 



The application of this method involves simply the 

 periodic emission from one of the ships of synchronous 

 signals, the other ship receiving them and reporting the 

 distance. Or each ship may alternately emit the signals 

 and make its own observations of distance. When A hears 

 the regulation fog signals of B the synchronous signalling is 

 commenced and the signals sent out, say, at intervals of two 

 minutes. Or the method might be applied under Board of 

 Trade regulations enjoining the periodic emission of 

 synchronous signals in thick or foggy weather. When the 

 vessels come within hearing of the submarine sounds the 

 Officer writes down the distances as his wireless operator 

 reports them to him. If they continue to show a constant 

 rate of approach even when the vessels draw near one 

 another there is danger. If the rate of approach diminishes 

 there is safety. If the A^essels are approaching so as to pass 

 close to one another the change of rate will be very marked 

 as the distance diminishes. The most valuable feature 

 of this method is that the sailor knows all along what time 

 must remain for action supposing collision is really 

 threatened. A rough determination of bearing completes 

 his observations and tells him how he must act. 



Trial of all these available methods should be made by the 



