is wired both to the switch arm s and to the connecting wire corresponding to that station, while the remaining terminal is joined to the common return wire r. Each station has its contact point mounted at the extreme left of the row, but is not connected in circuit; this point is intended to be covered by the switch arm after a conversation is finished, but as will be seen by referring to the diagram a station can be called while its switch arm is on any of the contact points. In Fig. 108 the switch at Station 2 is set for signaling Station 1. Supposing this switch was left in the position shown, Station 2 could be signaled by any one of the other stations; if, however, either Station 3 or 4 signaled Station 1, the bells in both Stations 1 and 2 would ring. Although this would be somewhat annoying to the party in Station 2, it would, nevertheless, be due to his own carelessness in not having his switch arm in its proper position.

A Battery and Battery Bells can be used in place of magneto generators and bells on intercommunicating systems if wired as in Fig. 109. The connections shown permit any station to signal any other station regardless of the position in which the switch arm at the station called has been left. Although but 3 stations are shown, any number of them can be connected, the number of connecting wires required being 2 in excess of the number of stations. Each station contains the same apparatus wired in the same manner, the transmitter battery b being retained as in the preceding cases.

The signaling battery serves for the entire system and is connected between the battery wire a and the common return wire c at any convenient part of the system. The battery bell e at each station is permanently connected to the contact point corresponding to its station, and the pivot of the switch arm s is wired to the push switch k in each case. The connections shown enable only the bell at the station called to ring; the bell in the calling station not being in circuit will not ring.

FIG. 109.-Wiring for an Intercommunicating System Using a Common Signaling Battery in Place of Magneto Generators

Although it is usually advisable to have both these bells operate in order that the party signaling may know his signal has been transmitted, it is not practicable to do so in this case.

An Exchange Communicating System can be had by wiring the stations as in Fig. 110. The central or exchange Station C is the only one that can be signaled from the other stations, but from this station any of the others can be signaled. The wires m and n connect with each of the sta

tions as shown, and from C there is a wire w to each of the other stations. A party at Station A or B signals Station C by closing the switch s; this closes the circuit containing the battery b and battery bell t in Station C and raises the party there. From Station C either of the other stations can be signaled independently by placing the switch arm v on the contact point corresponding to the station desired and closing the switch e.

FIG. 110.-Connections for an Exchange Communicating System

Station C can be signaled regardless of the position in which the switch arm v is left. It will be noted that no induction coils are used in this system and that the battery b in Station C furnishes current for both signaling and talking purposes.

Automatic Intercommunicating Systems are those in which the switch arm at each station is returned automatically to its normal calling position after a conversation is finished. The Ness system controlled by the Holtzer-Cabot Company is of this kind, and a telephone wall set fitted with

this automatic attachment is shown in Fig. 111; it can be connected to operate according to any of the intercommunicating methods previously described. The party using it moves the switch arm s to the contact point corresponding to the station desired, and when through returns the receiver

to the hook switch h. The motion of the hook switch when the receiver is hung upon it actuates the mechanism for restoring the switch arm to its normal calling position shown in Fig. 111.

This mechanism, Fig. 112, consists of a dog d, pivoted on the short arm of the hook switch h, which projects into a notch on a pawl p and lifts

the latter out of engagement with a ratchet wheel w when the switch hook is pulled down. The ratchet wheel w and the contact arm s being mounted on the same shaft with a spiral spring, the action just noted permits the spring to return

FIG. 112.-Details of the Automatic Attachment in the Wall Set Shown in Fig. 11I

the contact arm to its normal position. After the pawl p has been raised to a certain point, the dog slips out of the notch on it, permitting the pawl again to come in contact with the ratchet wheel w and be ready for the next use of the telephone. To prevent the pawl from engaging with the ratchet wheel before the contact arm s has reached its final position, the second dog g is provided; this is pressed by a spring so as to project under the pin k, carried on the pawl p, and holds p away from the ratchet wheel until s has traveled to its normal position. Then a cam on the ratchet wheel forces the dog g away from the pin k and allows the pawl to drop into position.