496 



NATURE 



\_March 25, 1880 



listening with the telephone, which is unhooked to apply 

 to the ear, and at the same time of taking notes on the 

 desk with the free hand. 



The Broadway system of telephones belongs to the 

 class of Pile Telephones, which allows these piles to be 

 used to call the attention of the subscribers by means of 

 ordinary bells, like the one in the desk, Fig. 4. 



The transmitter is Edison's carbon telephone, based 

 on the variations in electric resistance produced by 

 variations of pressure which the plate exercises when 

 we speak in front of the mouthpiece. The circuit is 

 formed by the pile, two Leclanche elements, the trans- 

 mitter, and a small Ruhmkorff coil. It constitutes the 

 primary circuit of the coil. The line and the receiver of 

 the other post are connected by the secondary wire of the 

 bobbin, a wire whose other extremity is connected with 

 the receiver of the post and with the earth. It follows 



that the line-currents are currents induced by the varia- 

 tions of activity of the current which traverses the primary 

 wire of the coil. This arrangement has the effect of 

 transforming into currents of tension the undulatory 

 currents of the transmitter, of rendering them less sensible 

 to the variations of resistance of the line, of facilitating 

 the adjustment and suppressing a part of the commutators, 

 the management of which might cause mistakes. 



The receiver is a Phelps telephone, analogous to the 

 Bell telephone, but the magnet of which is turned round 

 in the form of a ring, which renders its management very 

 easy (Fig. 4). In the position of repose or waiting, the 

 telephone hangs on its hook, and by this fact alone, it 

 comes into contact with a part forming a commutator, 

 which suppresses all the telephonic part of the circuit, in 

 order that the bell alone may intervene. Everything is 

 thus ready for a call. 



Fig. 1. — Interior view cf the administration of the Merchants' Telephone Exchange, New York. 



The telephones of the central post, speaker and receiver, 

 are analogous to those of the subscribers ; but to facilitate 

 the management of these apparatus the speaker and 

 receiver are mounted on the same steel stem, somewhat 

 bent to serve as a handle, as in Fig. 2, and forms at the 

 same time the magnet of the receiver. 'We may now 

 follow all the series of operations. Suppose subscriber 

 No. 731, whom we will call Edward, wishes to correspond 

 with 511, whom we will call John. Edward begins by 

 pressing on a small knob on the right side of the desk, 

 Fig. 4. As the telephone is suspended it follows that in 

 that position the current of Edward's pile traverses the 

 line and a small electro-magnet in the central office ; the 

 electro-magnet, becoming active, detaches a small door 

 (Fig. 2), which falls with a noise sufficient to call the 

 attention of the employe, and exposes the number 731. 

 The employe then places himself in communication with 

 Edward, by placing the wire which corresponds to his 

 telephone on a longitudinal copper bar also connected 



with Edward's line. The conversation then begins with 

 the useful shout of hallo ! hallo ! Edward asks the 

 employe 1 to place him in communication with No. Jii. If 

 No. 511 is free at the moment the employe presses a knob 

 after having connected the wire of No. 511 with the 

 knob. The bell of John is set agoing, and when he him- 

 self is ready to correspond he presses the knob of his 

 bell, which causes the door of his number to fall. By 

 then placing a wire of communication directly between 

 the two horizontal bars which correspond to the wires of 

 Edward and John, direct communication between these 

 two correspondents is established. If at this moment the 

 employe is obliged to withdraw his telephone the com- 

 munication between Edward and John is secret. If while 

 these two are in conversation No. 42, James, wishes to- 

 correspond with John, for example, the employe may join 

 in the conversation of the two interlocutors just like a 

 servant announcing a visitor. If required, conversation 

 may be established between the three subscribers. When 



