130 nature's flMractes. 



This vibrator is so arranged in relation to the 

 battery that whenever the key belonging to it 

 is depressed the current all through the line 

 is rendered vibratory. There is also in circuit 

 at each end of the line a harmonic relay, that 

 is tuned in accord with the vibrating reed of 

 the sender. If either key belonging to this 

 part of the system is opened, as in the act of 

 sending a message, these harmonic relays, be- 

 ing tuned in sympathy with the sending-vi- 

 brator, will respond, thus sending Morse char- 

 acters made up of a tone broken into dots and 

 dashes. This tone can be read directly from 

 the relay, or, as is usually the case, it causes 

 the sounder to operate in the common way. 



You will at once inquire why the ordinary 

 Morse instruments in the local offices are not 

 affected by these vibratory signals, and also 

 why the harmonic instruments at the end of- 

 fice are not affected by the working of the 

 local offices. The local office does not open the 

 circuit entirely, but simply cuts out a resist- 

 ance by the operation of the special harmonic 

 key. When a resistance is thrown into an 

 electric circuit it weakens the current in pro- 

 portion to the amount of resistance interposed. 

 You will see that there is some current still 

 left in the line when the key is open, but the 

 spring of the relay at the local office is so ad- 

 justed as to pull the armatures away from the 

 magnets whenever the current is weakened by 



