Nov. 1st, 1887.] 



SCIENTIFIC NEWS. 



205 



B's attention by his own bell ringing, lifts his receiver off 

 its hoolc, and speaks into the transmitter; the required con- 

 versation follows, and at its close both parties hang up 

 their receivers, and thereby again put into the line-circuit 

 the calling apparatus ready for the next occasion. Figs. 13 

 and 14 represent diagrammatically an arrangement which 

 makes the necessary connections on lifting the receiver oft' 

 or putting it on the hook. Both positions are shown ; the 

 lettering of the parts being identical in each. H is a brass 



fixed in the case, and a length of flexible tube held to each 

 ear. When the instrument is not in use, the tubes hang in 

 hooks on each side of the instrument, and so operate two 

 switches, one of which connects the line to the bell or 

 receiver, while the other closes the transmitter circuit, the 

 two switches thus performing together the same functions 

 as the one switch in the Bell-Blake instrument. The con- 

 nections are shown in Fig. 15. K is the ringing key, S the 

 switches, the right-hand switch completing the transmitter 



t/i a^^x^&r^uLttct^ 



Fig. 14. Speaking Position — Telephone Receiver off 

 Hook. 



hook, projecting through the side of the case, pivoted inside, 

 and having a spiral spring attached, which, when the weight 

 of the receiver is oft' the hook, pulls it into the " speaking " 

 position. The inner end of the hook is a kind of cam, and 

 it is connected to one pole of the battery in the transmitter 

 circuit. In the ringing position, the spring B, connected to 

 the line-wire, presses against the spring C, and is con- 

 nected through it to the bell and ringing-key or magneto. 

 The spring A, leading to the receiver and the secondary 

 wire of the induction coil, is disconnected and out of cir- 

 cuit, and the primary wire and battery are also discon- 

 nected. In this position of the switch it will be seen that a 

 current from the line will pass through the bell-coils, and 

 therefore make the bell ring ; or if the ringing-key or 

 magneto is worked, the current from it will go to the line. 

 In the " speaking " position the spring B is pressed against 

 the spring A, and the line is thus connected to the secondary 

 wire and the telephone receiver; the circuit containing the 

 primary wire of the induction coil, the battery, and the 

 transmitter is also closed, and thus any current from the 

 line will pass through the receiver, and any current in- 

 duced in the secondary wire will pass out to line, and to 

 the distant receiver. 



Several other forms of automatic switch are in use, per- 

 forming the same operations in other ways. That illustrated 

 is practically the one used with the Blake-Bell combination 

 instrument ; in the Gower-Bell instrument used by the Post 

 Office, two receiving tubes are used, the receiver being 



Fig. 15. Connections of Bell-Blake Instrument. 



circuit, the left-hand one putting the line into connection 

 with either the bell or the speaking instruments. I is the 

 induction coil, P and S being the primary and secondary 

 wires, and D is the receiver ; B is a relay which completes 

 the bell circuit when a current passes through it, the bell 

 being actually rung by one cell of the battery. This 

 arrangement is used for long circuits, on which the battery 

 current is too weak to ring the bell direct. On short lines 

 the relay is not wanted, and the bell-coils are connected in 

 its place. Fig. 16 shows a perspective view of the instru- 

 ment with the cover removed. This view does not show 



Fig. 



[6. Perspective View of Bell-Blake Instrument 

 with the cover remo\ed. 



the microphone, which is fitted to the underside of the 

 cover. Its form is shown in Fig. 15, on the right, and 

 the details have been already illustrated in Fig. 10 (page 

 181). 



