16 Prof. J. Joly on Scientific 



hundredths or even thousandths of a second. In order to 

 transmit 20 words per minute by code about 100 compressional 

 waves are required per minute, and to transmit speech 

 several thousands of waves. 



This power is, of course, applied electrically, an armature 

 being excited by a powerful alternating current having a 

 frequency of about 500 per second. 



It is remarkable that this instrument, in spite of the great 

 inertia and accelerations involved, can act as a receiver 

 to sound waves reaching the ship through the water ;. 

 functionating then as a generator. Hence it is only necessary, 

 when the oscillator is being used both for the transmission 

 and reception of sound, to set over a switch with each change 

 in the nature of the operations required. The sounds may 

 also be received by ordinary microphone as fitted for the 

 submarine bell. (An interesting account of the improved 

 oscillator is issued by the Submarine Signal Company.) 



In an early test the oscillator was lowered 12 feet off 

 the Boston lightship. The signals were plainly heard by 

 microphone 31 miles away. They have been emitted also 

 from moving ships and heard more than 20 miles away. 

 It is evident that on vessels and in situations where an 

 alternating current of sufficient power is available the use of 

 this new device possesses great advantages. For not only 

 is the range of the sound greatly increased over that claimed 

 for the bell, but code signals can be easily transmitted. 

 And there are also new possibilities as regards synchronous 

 signalling. A vessel moving at the high speed of 25 knots 

 may learn her distance from the land, the bearing of the 

 signal station, and hence the correct course to steer, more 

 than an hour before she makes her harbour. Remember, too, 

 that this information comes in in any weather. It has not to 

 be listened for in the open but is quietly whispered in the 

 cabin. 



Of great interest, too, are the applications of the oscillator 

 as a depth-finder and as a protection against icebergs. In 

 both cases the reflexion of the sound and its return to the 

 observer are used. 



The depth-finder is admirably simple. Imagine a com- 

 mutator-wheel with one conducting segment leading to 

 the armature of the oscillator. Two brushes touch this 

 wheel, one connected to the alternating current generator, 

 and the other to the telephone-receiver. As the wheel is 

 rotated the oscillator is excited while the brush connected 

 with the source of current is passing over the conducting 

 segment. Excitation then ceases and the sound from the 



