October 12, 1911] 



NATURE 



487 



After conversation, both subscribers hang up their 

 receivers, this action momentarily earthing both wires 

 of each loop. In the case of the originating sub- 

 scriber, the effect of this is to "clear," and to restore 

 to normal his mechanism at the exchange. 



At the exchange end of each loop a separate switch 

 is placed, the mechanical outlines of which are given 

 in Fig. 2 and the electrical connections in Fig. 3. 

 Considering the former, we have an upright steel 

 shaft L which has on its upper portion a series of 

 horizontal teeth, cut the whole way round the shaft. 

 VM is an electromagnet having a pawl on the end 

 of its armature, the latter being pivoted at PP. When 

 VM is energised, this pawl lifts the shaft by means 

 of one of the horizontal teeth. Below these teeth 

 the diameter of L is much increased, and on the 

 surface of the cylinder thus formed, a series of vertical 

 grooves or teeth are cut. RM is another electro- 

 magnet, the armature of which, pivoted at PP, carries 

 at its extremity a second pawl. When this armature is 

 attracted L is forced round a tooth. The double pawl 

 O, engages with both the horizontal and vertical teeth, 



VERTICAL LINE 



COHDEHSLR 



-Subscribers Switch— Connection: 



and prevents the return of the shaft after its move- 

 ments in an upward and rotary direction. Each of 

 these two electromagnets is placed, in turn, in the 

 local circuit of a relay at the required time, and 

 whenever an impulse passes through VM the shaft L 

 is raised a tooth, whilst an impulse through RM 

 causes the shaft to be rotated a tooth. They are there- 

 fore termed the "vertical" and "rotary" magnets. 

 CM is the clearing magnet ; when this is energised, its 

 armature strikes the double pawl Q and causes it to 

 release the shaft. The latter, in its previous turning 

 movement, winds up a spring, and on its release the 

 spring brings it back, and by its own weight the shaft 

 falls to its normal position. 



At the lower end of L two arms are carried which, 

 when desired, make connection with any one of a 

 series or "bank" of contacts. The essential parts of 

 these contacts and of the arms are best seen in the 

 right-hand lower corner of Fig. 2. First we have a 

 thin semicircular strip of fibre or other insulating 

 material. On the upper surface of this ten thin 

 strips of metal are placed radially, and on the under 

 surface ten other similar strips are placed. To an 

 upper and a lower metal piece the lines of each loop 



NO. 2189, VOL. 87] 



are connected, so that one semicircular piece carries 

 th- twenty contacts of ten loops. Above this horizontal 

 row of ten circuits a second, third, and tenth semi- 

 circular pieces are placed, each being separated from 

 its upper and lower neighbours by further insulation. 

 We have thus the contacts of a hundred loops 

 arranged in ten layers of ten each. 



As already seen, every subscriber has one of these 

 switches, and the banks are all multipled together. 

 That is, No. 5S line is brought to the fifty-eighth 

 position on the banks of all the hundred switches 

 constituting the exchange. 



The two arms, or " wipers " — so called from their 

 brushing or wiping action in passing over the contacts 

 — each consist of two metallic strips, insulated from 

 each other and from the shaft, the outer ends having 

 a slight inward tendency, so that when they engage 

 the two springs of a loop there is sufficient friction to 

 ensure electric contact. 



As will be seen from Fig. 2, there are two banks 

 of contacts, one above the other, and two arms or 

 wipers to engage with them. On the lower bank are 

 the hundred loops as 

 already detailed. The upper 

 bank is employed for 

 giving the " busy " signal. 

 Its arm has the two con- 

 tacts connected together, 

 so that only a single con- 

 nection is made in any one 

 of the hundred positions. 

 Like the lower bank, these 

 are multipied on all the 

 switches of the exchange. 

 There are indeed, two mul- 

 tiples, the line multiple and 

 the "busy," or "engaged," 

 multiple. In the normal 

 position of the shaft 

 the wipers are just to 

 the left of the banks 

 and just beneath them. 

 When L is raised one, 

 two, &c, teeth, the 

 wipers rise to the level 

 of the first, second, &c, 

 row. A single rotary 

 movement then brings 

 the wipers to the first 

 loop in the row ; two 

 three, or more rotary movements bring the 

 wipers to corresponding loops on that horizontal 

 level. 



Returning to the upper mechanism of the switch. 

 BB is an arm pivoted at PP, and carrying on its 

 left a four-lever switch. On its right it engages with 

 the escapement U, which is carried on a long exten- 

 sion of the armature of the switch-magnet SM. A 

 spring- S keeps the right-hand end of BB against U. 

 When SM is actuated, the movement of attraction and 

 release allows BB to slip forward one step in the 

 escapement, and causes E, F, G, and H to quit their 

 first contact and move to the second. The action of 

 this " side-switch " is to bring the various pieces of 

 apparatus into action at the required time. A second 

 movement of SM allows BB to move forward an- 

 other step in U and brings the side-switch into the 

 third position. Any further movement of SM does not 

 affect BB. When, however, the clearing magnet CM 

 is actuated, the movement of Q restores BB to its 

 original position, the escapement springs opening and 

 allowing the right-hand end to pass. The side- 

 switch thus returns to position 1. 

 The electrical conditions are shown in Fig. 3. VM, 



ROTARY LINE 



