e"^oi 



Signalling and Safety at Sea. 21 



considerable speeds ; so that they may cover a half-knot 

 in l-o- minutes, or even in one minute when the relative velo- 

 cities of the vessels are taken into account. As the mutual 

 avoidance of such vessels cannot safely be left to less than 

 the last minute, the sensitiveness of the method is quite 

 adequate to the use required of it. 



It will not, probably, be superfluous to say something as 

 to the available means of submarine signalling between ship 

 and ship as apart from the mere reception on the ship of a 

 submarine signal sent from the shore. The latter subject we 

 have already considered, but nothing has been said as to the 

 emission of submarine signals from the ship. 



There is first of all the use of the bell. The sound of the 

 bell may normalty be taken as carrying 7 or, at least, 5 

 miles. It gives a sharp, unmistakable sound ; and the 

 apparatus concerned has the advantages of compactness and 

 simplicity of construction. Its application to ships would 

 appear to involve the provision of a recess somewhere in the 

 ship's bottom. The bottom is assuredly the best position ; 

 for the radiation of the sound is then not interfered with in 

 any direction by the ship herself. The provision of the 

 recess is a protection to the bell, which is supposed to be 

 raised into the recess and housed therein when not required 

 for use. This construction has, I understand, already been 

 applied to submarines. 



The rival sound-signalling machine is the Fessenden 

 Oscillator. This is an instrument for which a much greater 

 range is claimed, and is, in addition, highly adapted for 

 transmission of code signals. 



Whether bell or oscillator are employed we may suppose 

 the signals completely controlled from the room of the wire- 

 less operator and the easy possibility of securing mechanical 

 control of the signals, so that by clock-work their emission 

 may be accurately regulated and timed to the signals sent 

 out by wireless in the setherial medium. We may, in short, 

 discuss the use of synchronous signalling in avoiding 

 collision, with our minds at ease as to the complete practical 

 possibility of putting the method into operation. Both the 

 bell and the oscillator have, in fact, already been applied to 

 moving vessels. 



We shall assume that ships navigating in fog or thick 

 weather are required by (future) Board of Trade regulations 

 to emit a certain low-power wireless signal at intervals, say, 

 of 5 minutes, and that when two ships become aware of 

 each other's signals they may, if they deem it necessary, 

 exchange the usual code signals giving course and speed. The 



