1879.] 071 Multiple Telegraphy. 197 



Its apjilication enables really more than double the amount of 

 work being dene to that wliicli tlie wire (if an ordinary land line) 

 wonld perform wlien working singly. This arises from the fact that 

 no interruption ensues from repetitions being required or questions 

 asked, but the messages pass in a continuous stream in opposite 

 directions almost without let or hindrance. 



I would just mention another fact in answer to any who arc 

 surprised at errors taking place in the transmission of messages. The 

 signals representing certain letters are very similar, and it is very 

 easy for a faint dot to be missed or a short dash to be misinterj)reted 

 for a dot, and as the difference between the letter t (represented by a 

 dash) and r (represented by a dot, dash, dot) is simply two dots, you 

 will not be surprised that a message, informing some friends of the 

 arrival of a party of ladies, " all right," was delivered as, " all tight." 

 And, again, a friend of mine in Manchester, whose wife wished to 

 inform him that the " rash was all gone," was astonished to receive an 

 intimation that the " cash was all gone." Many of these errors are 

 simply due to the failure of a dot or the shortness or breaking of a 

 dash, and the wonder is that with more than one hundred million 

 messages which are despatched every year in this country the per- 

 centage of errors is not greater than the small amount it is. I hope 

 that, after the practical illustration you have just had of the extreme 

 care and exactitude which is attendant on the accurate receipt of 

 signals, you will deal lightly with errors of conversion of words such 

 as " rash " into " cash," '' right " into " tight," &c. 



So far as regards duplex telegraphy. 



We have now to deal with another class, and that is called diplex 

 telegraphy. Duplex telegraphy means sending two messages in 

 opposite directions at the same time ; diplex means sending two 

 messages at the same time in the same direction. I have here two 

 little instruments which give out their signals in musical tones, and I 

 have also two keys attached to a battery in connection with them. 

 There is only one wire between them. If I press down, say, key No. 1 

 I call up the sounder which emits a deep tone ; if I press down key 

 No. 2 I obtain a response from the sounder with a tone an octave 

 higher. If I press both keys down at the same time both sounders 

 answer, and whichever key is depressed it is always answered by its 

 proper sounder. This power of sending two signals or messages at 

 the same time in the same direction is called diplex telegraphy. 



It is difficult to explain how this is performed without the aid of 

 a diagram, and it really requires some amount of courage to attempt 

 the feat. Currents of electricity are developed in two ways : they 

 differ in the direction in which they flow and also in their strength. 



The key on my right hand simj)ly reverses the direction in which 

 the currents flow every time it is dej^ressed ; the other key simply 

 increases the strength of the current flowing, whatever may be its 

 direction. The relay here employed, which is connected to the deep- 

 toned sounder, responds to a reversal of the current whatever its 



