WILLIAM SIEMENS, F.R.S. 327 



lent to about twelve currents or primary impulses per second. In 

 transmitting these impulse-currents simultaneously from both 

 ends of the line, it must not be imagined, however, that they pass 

 each other in the manner of liquid waves belonging to separate 

 systems ; such a supposition would involve momentum in the 

 i'l< r trie flow, and although the effect produced is analogous to 

 such an action, it rests upon totally different grounds namely, 

 that of a local circuit at each terminus being called into action 

 automatically whenever two similar currents are passed into the 

 line simultaneously from both ends. In extending this principle 

 of action quadruplex telegraphy has been rendered possible, 

 although not yet for long submarine lines. 



The minute currents here employed are far surpassed as regards 

 delicacy and frequency by those revealed to us by that marvel of 

 the present day, the telephone. The electric currents caused by 

 the vibrations of a diaphragm acted upon by the human voice 

 naturally vary in frequency and intensity according to the number 

 and degree of those vibrations, and each motor current in exciting 

 the electro-magnet forming part of the receiving instrument 

 deflects the iron diaphragm occupying the position of an armature 

 to a greater or smaller extent according to its strength. Savart 

 found that the fundamental la springs from 440 complete vibra- 

 tions in a second, but what must be the frequency and modula- 

 tions of the motor current and of magnetic variations necessary 

 to convey to the ear through the medium of a vibrating armature, 

 such a complex of human voices and of musical instruments as 

 constitutes an opera performance ? And yet such performances 

 could be distinctly heard and even enjoyed, as an artistic treat, by 

 applying to the ears a pair of the double telephonic receivers at 

 the Paris Electrical Exhibition, when connected with a pair of 

 transmitting instruments in front of the footlights of the Grand 

 Opera. In connection with the telephone, and with its equally 

 remarkable adjunct the microphone, the names of Reiss, Graham 

 Bell, Edison, and Hughes will ever be remembered. 



Considering the extreme delicacy of the currents working a 

 telephone, it is obvious that those caused by induction from 

 neighbouring telegraphic line wires would seriously interfere with 

 the former, and mar the speech or other sounds produced through 

 their action. To avoid such interference, the telephone wires if 



