No. 6.] president's address b. a. a. s. 345 



station, after having produced their extremely slight but certain 

 effect upon the receiving instrument. So perfect is the channel 

 and so precise the action of both the transmitting and receiving 

 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 under the superintence of Dr. Muirhead, its trans- 

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

 minute, being equivalent to about twelve currents or primary 

 impulses per second. 



The minute currents here employed are far surpassed as re- 

 gards 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 hu- 

 man 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 receiv- 

 ing instrument, deflects the iron diaphragm occupying the posi- 

 tion 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 fre- 

 quency 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 performance. And 

 yet such performances could be distinctly heard and even en- 

 joyed as an artistic treat by supplying to the ear a pair of the 

 double telephonic receivers, at the Paris Electrical Exhibition, 

 when connected with a pair of transmitting inrtruments in front 

 of the foot lights of the Grand Opera. In connection with the 

 telephone, the names of Reiss, Graham Bell, Edison, and Hughes 

 will ever be remembered. 



Regarding the transmission of power to a distance the electric 

 current has now entered the lists in competion with compressed 

 air, the hydraulic accumulator, and the quick running rope as 

 used at Schaffhausen to utilise the power of the Rhine fall. 

 The transformation of electrical into mechanical energy can be 

 accomplished with no further loss than is due to such incidental 

 causes as friction and the heating of wires ; these in a properly 

 designed dynamo-electric machine do not exceed 10 per cent, as 

 Vol. X. w No. 6 



