ADDBESS. 9 



wires, 5 mm. in diameter, by nearly 5,000 kilometres in length, con. 

 fined electrically by a coating of guttapercha about 4 mm. in thick- 

 ness. The electricity from a small galvanic battery passing into 

 this channel prefers the long journey to America in the good con- 

 ductor, and back thi'ough the earth, to the shorter journey across the 

 4 mm. in thickness of insulating material. By an improved arrange- 

 ment the alternating currents employed to work long submarine cables 

 do not actually complete the circuit, but are merged in a condenser at 

 the receiving station after having produced their extremely slight but 

 certain effect upon the receiving instrument, the beautiful syphon recorder 

 of Sir William Thomson. So perfect is the channel and so precise the 

 action of both the transmitting and receiviug instruments employed, that 

 two systems of electric signals may be passed simultaneously through the 

 same cable in opposite directions, producing independent records at either 

 end. By the application of this duplex mode of working to the Direct 

 United States cable nnder the superintendence of Dr. Muirhead, its 

 transmitting power was increased from twenty-five to sixty words a 

 minute, being equivalent 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 electric 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 quadruples 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 vibrations in a 

 second, but what must be the frequency and modulations 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 perforroftnce ? 

 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 tele- 

 phonic 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 telei^hone, and with its equally remarkable 



