NATURE 



[October 12, 1911 



KM, CM, and SM are the electromagnets already 

 described. VR and RR are the vertical and rotary 

 relays, mounted side by side. The armatures of these 

 when attracted act upon the contacts shown between 

 them. If VR is energised, g is pressed forward to- 

 gether with r. The latter then makes contact with 

 the centre spring s, but the movement is not suffi- 



HI 





Hzr 



FlG. 4.— Earthing of Ve 



-Earthing of Rotary Lin 



cient to bring g and x together. When RR is 

 actuated x is pressed forward, carrying u with it to 

 make contact with s, but x does not reach g. When 

 both relays are energised, g and x make contact in 

 addition to the other two. Two other relays, J and K, 

 are mounted together, and act upon the springs shown 

 between them. 



VL 



We are now able to trace the results of the sub- 

 scriber's call. He desired No. 58. By the first move- 

 ment of his disc we saw that he earthed the vertical 

 line five times and the rotary line once. Fig. 4 gives 

 the result of this. By the earthing of the vertical 

 line (as indicated by the arrow-head) a path, shown 

 as a heavy line, is open to the battery from its positive 

 pole through one coil of K and the ver- 

 tical relay and line to earth. This current 



actuates both K and VR, as shown by 



the shading. The spring r being earthed 

 at 5, a second path, shown dotted, is open 

 to the batterv via VM and the lever E 

 of the side-switch. The shaft L is there- 

 fore raised five teeth, corresponding to the 

 number of current impulses passed over 

 ■?i the vertical line. The earthing of the 



rotary line (once), as shown in Fig. 5 by 

 the heavy line, actuates K by its lower 

 coil and RR. The latter closes s and u 

 and completes the circuit (shown dotted) 

 of the switch magnet SM. This brings 

 the side-switch into position 2. 



The calling subscriber now inserts his 

 finger in the eighth hole, brings the disc 

 round, and then liberates it. The vertical 

 line is then earthed eight times, and the 

 rotary once. As the side-switch is in 

 position 2 a circuit is open to the eight 

 currents through the upper coil of K, 

 VR, and the vertical line. K and VR are 

 actuated, the latter connecting r and s 

 and providing a second path from 

 the battery through the rotary mag- 

 net, switch-lever E, and earth. The state of 

 affairs is precisely as in Fig. 4, saving that KM 

 is substituted for VM. The rotary magnet armature 

 rotates the shaft (already on the level of the fifth 

 row), and brings the wipers on to the eighth contact 

 in that row. The final earthing of the rotary line 



Z ! 



Each of these two 

 relays has two 

 coils. If current 

 circulates in one 

 coil the armature 

 responds : simi- 

 larly if current 

 flows in both coils 

 in the same direc- 

 tion. If, how- 

 ever, the two 

 currents are in 

 opposite d i r e c- 

 tions, they nullify 

 each other's 

 effects, and the 

 armature is not 

 attracted. The 

 movement of J's 

 armature breaks 

 the contact be- 

 tween b and a, 

 and makes a new 

 one between b 

 and c. Similarly 

 with K : c breaks 

 from / and makes 

 with d. GMisthe 

 generator magnet. 



When this is actuated the two long springs move 

 upwards, disconnecting from the lowest and bringing 

 the generator on to the levers G and H of the side- 

 switch, and thence (when in position 3) via the line 

 wiper to the desired subscriber's line. 



NO. 2189, VOL. 87] 





A 



tt=! 



r=3J 





repeats the operation shown in Fig. 5, and shifts BB 

 another tooth in the escapement I , thus bringing the 

 side-switch into position 3. 



The wipers are now on the contacts of the desired 

 loop and the calling subscriber depresses his push- 



