in the center, in obedience to the impulses sent from the subscriber's telephone, and bring the three pairs of "wiping fingers" attached thereto into connection with the

hundred telephones. The function of the selector is to connect the calling telephone with the connector in the proper group, which in turn connects with the telephone desired in that group. This is the case in exchanges of one thousand capacity or less. In larger exchanges a second collector is employed. This is an intermediate switch, and divides the work of selection with the first selector.

Trunk-Selecting System

The trunking system employed is very much akin to that now generally used in manual practice and, therefore, needs no description here. It may be said, however, that the selection of trunks is automatically accomplished, the "wiping fingers" on the shaft of the selector switch passing over all busy contacts and stopping at the first idle point.

AUTOMATIC TELEPHONE SWITCH.

Side View.

brass contacts, which, arranged in three semicircular banks, constitute the lower half of the switch.

The upper of these banks, known as the "busy bank" serves to indicate busy lines in the automatic selection of trunks. The lower two are "line banks," to which the line wires connect, and over which the conversation is held.

Two classes of switches are employed, one known as "selectors," of which there is one for every telephone connected with the exchange, and the other as "connectors," of which there are ten for every hundred selectors and which are in groups each capable of connecting one

INTERIOR OF WALL TELEPHONE.

attachment; charging machines; power board, on which are mounted the usual knife switches, circuit-breakers, voltmeters, ammeters, etc., necessary for

controlling and measuring the current; and a "tell-tale" board.

This last consists of a number of 8candle-power lamps mounted on a marble panel, together with a magneto bell. In case of a short circuit or "ground" on any line, the bell rings and the lamp on the panel glows. The position of this lamp instantly indicates to the attendant the exact location of the trouble, and ofttimes enables him to rectify it before the subscriber is aware that there has been any trouble.

The automatic switches are mounted on steel shelves, twenty-five to the shelf, each board containing four shelves of first selectors, and one shelf of connector switches. This is the arrangement for a system of 1,000 stations. In a 10,000-station system, the board is made up of six shelves, four of first selectors, one of second selectors, and one of connector switches. The floor space occupied by such a switchboard is II feet 6 inches by 12 inches. The switchboard is made of steel angles and is rigidly braced.

A very important feature of the automatic switchboard is that it can be increased to any capacity by simply adding new sections with the desired number of switches mounted thereon, without in any way interfering with existing conditions. Ninety-five per cent of the electric contacts and connections are made at the factory; consequently better results are secured, as well as time and expense saved in installation.

Advantages of the Automatic System

I. A switchboard has no operators; and thus one of the large fixed charges incident to manual-exchange operation is eliminated.

2. There being no operators, the automatic exchange can be located in less expensive quarters than the manual. No reading or retiring rooms are needed, no lockers, no lavatories; and the cost of fuel and lighting is reduced.

3. One switchboard attendant, for testing and keeping apparatus in order for 1,000 subscribers, is all that is needed in the automatic practice.

4. The cost of maintenance and interior equipment is no greater, and in large exchanges is less than in the manual exchange.

5. The service which the automatic system gives, unlike that of the manual system, is absolutely secret, each subscriber having a "private wire" on which to transmit his communi

AUTOMATIC TELEPHONE SWITCH.
Rear View.

do not make errors nor gossip; are never weary or sleepy; are not interested in subscribers' affairs; and are not impudent.

8. The complexity of the automatic exchange does not increase proportionately to the increase of size, as is the case with manual exchanges, where the cost of giving service is much more per subscriber in large than in small exchanges. The cost of operation in the automatic exchange is fixed. An increase is merely a matter of adding new telephones and switches, the cost of operation being the same per subscriber.

9. The automatic switch is thoroughly cosmopolitan in its nature, no interpreter being needed by the foreigner in a country where the automatic exchange is located, any person being able to secure the desired connection by simple rotations of the dial.

10. The same number of automatic switches are always at work, night and day.

ac

II. Quick connections, instantaneous commodations, prompt answers, accuracy, and promptness, with the busy signal given when subscriber called is busy.

S

INCE the new Holland submarine torpedo-boat, the Fulton, spent a comfortable night on the bottom of Narragansett Bay, the public have felt that Jules Verne and his fabled Nautilus are a good deal of a reality.

On the evening following the speed and fire tests, the Board of Inspection appointed by the Navy Department decided to test the Fulton as to the comfort of the men who had to live in her. It was therefore decided that the boat should spend the night at the bottom of the bay.

This was the first test ever made under naval supervision, to determine whether men can live aboard a submarine boat under water as safely as on the surface.

All the necessary preparations were made, and at seventeen minutes to eleven, the Fulton sank with nine men aboard.

One of the features of the crew's experience was the distinctness with which sound was conveyed under water. Early in the morning the submerged crew were awakened by what was afterwards explained to be the Fall River steamer touching at Newport on its way from New York. Although the steamer did not pass within a mile of the submerged Fulton, several of the crew of the submarine were awakened by her plowing through the water.

If the spark coil is fitted with a circuit-closing attachment, as shown on the left-hand end of the coil in Fig. 1, it is not to be interfered with in any way when making the tests.

Where each burner is connected to a separate wire, as it should be, the trouble can easily be found by testing each wire. When the defective wire is found, it is cut out of the circuit and the other wires allowed to work again. Then go to all the burners and find out which one does

not work, and very likely the trouble will be found on the burner or jet. After the burner has been fixed, it can be put into service again by connecting its wire to the circuit of the battery.

To make this clearer, refer to Fig. 1, in which C is the terminal of the separate burner wires. Now suppose that the burner X is short-circuited, and that the burner Y is all right. The wires from the burners X and Y, which are connected at C to the battery circuit, would be separated, and the receiver terminals connected to the circuit wire A

and the burner wire X at N. At the time of connection and disconnection, a click would be heard; and, as the wire is defective, it is cut out of the circuit, while the other wire from the burner Y, which is not short-circuited, is connected to the wire A. Upon examining the burners, it will be found that burner X is out of order; and when repaired its wire N can be connected to wire A at C again, and everything will work all right. Electric Bell Circuits

Fig. 3 shows a method for detecting grounds in bell circuits or circuits where the ground is not used. If a click is heard in the receiver when the connection A B is made, there is a ground on the wire A'; and when the connection is made at A' B and the click is heard, the wire A is grounded. The contact be

tween the gas pipe and the receiver terminal must be very good.

Fig. 4 simply shows the connection for testing a bell circuit for leakage.

It very often happens that an electrician is alone when repairing or installing electric bells, and he cannot tell whether the bell rings or not when the contact is made; but, by using the telephone receiver, it is possible to tell just what the bell is doing when the button is pushed. Place the terminals of the telephone receiver on the contacts of the push button, and press the button several times. If a buzzing sound is heard when the contact is broken, the bell rings all right, provided that the hammer is properly adjusted. If no sound is heard at all, the circuit is broken; and if only a clicking noise is heard, the bell is not properly adjusted, or the batteries are not sufficiently strong to ring the bell.

There are a great many other uses to which the telephone receiver can be put, and one of these instruments should be in the hands of every electrician engaged in this class of work.