SCIENCE IN RELATION TO THE ARTS. 57 



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 vibra- 

 tions 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 four hundred and forty 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 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 foot-lights of the Grand 

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

 able adjunct the microphone, the names of Riess, Graham Bell, Edi- 

 son, and Hughes will ever be remembered. 



Considering the extreme delicacy of the currents working a tele- 

 phone, it is obvious that those caused by induction from neighboring 

 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 suspended in the air 

 require to be placed at some distance from telegraphic line wires, and 

 to be supported by separate posts. Another way of neutralizing inter- 

 ference consists in twisting two separately insulated telephone-wires 

 together, so as to form a strand, and in using the two conductors as a 

 metallic circuit to the exclusion of the earth ; the working current 

 will, in that case, receive equal and opposite inductive influences, and 

 will, therefore, remain unaffected by them. On the other hand, two 

 insulated wires instead of one are required for working one set of in- 

 struments, and a serious increase in the cost of installation is thus 

 caused. To avoid this, Mr. Jacob has lately suggested a plan of com- 

 bining pairs of such metallic circuits again into separate working pairs, 

 and these again with other working pairs, whereby the total number 

 of telephones capable of being worked without interference is made to 

 equal the total number of single wires employed. The working of 

 telephones and telegraphs in metallic circuit has the further advantage 

 that mutual volta induction between the outgoing and returning cir- 

 rents favors the transit, and neutralizes, on the other hand, the retard- 



