The police system that was used throughout the grounds of the Pan-American Exposition for the police department, was a decided departure from the old forms of circuit-telegraph signaling systems and was one of the most interesting features of the show to city electricians, police-department chiefs and other visitors interested in municipal police matters. The system, which was placed in use by the Municipal Signal company of Chicago, combines a signaling apparatus with a telephone on ordinary telephone-line construction. This system was leased by the exposition company and was used throughout the grounds during the entire season for the police and guard-department use.
The system was divided into three stations, in which all reports were received; Fig. 1 shows the central-office equipment at station No. 1, located in the Service building. This was a board for 50 patrol-box circuits and 10 private-telephone lines. These boards are provided with two sets of indicators for each line and patrol box. The regular officers' report signal is a shutter-drop, and one for each line is placed in the middle of the face of the board above the corresponding number of spring-jacks. In the center of the board are mounted the telephone-line visual signals, to which, in this case, were connected the private telephone lines from the commandant-of-police's office, the sergeant's office and the captain's office, the lines to the substations, and also trunks to the main telephone exchange. Immediately below the visual signals are mounted the clearing-out signals. Above the regular reporting signals are mounted a set of polarized ringers with gongs, for the emergency or wagon-call signal; each set of bells is provided with a small numbered indicator which corresponds in number with the station with which it is connected, and indicates which bell was rung.
The board is equipped with a complete operator's telephone and is also provided with a portable desk telephone, which may be connected as a duplicate of the regular operator's set. It also has a sufficient number of connecting cords and plugs, so that any line may be connected with another, and connection made between the patrol boxes, the offices and the public-exchange subscribers.
Immediately in front of the plugs, on the plug shelf, are mounted a set of listening buttons, one for each line. When an officer reports, the operator presses the correspondingly numbered listening button, which directly throws into circuit the operator's telephone, thus avoiding the use of the connecting plugs. Provision is made for using a power generator, and a hand generator is provided for emergency use.
Fig. 2 shows a sub-station desk switchboard in one of the tents in the guard station No. 3. This sub-station board is an ordinary roller-top desk, and equipped for 30 patrol-box circuits and 10 private telephone lines. Station No. 2, located in the Dairy building, was provided with a main-office switchboard, the same as in station No. 1. The three station switchboards were connected with direct-wire trunk lines, so that connection could be made from any of the patrol boxes connected with any of the boards, direct to any of the other stations, or any of the other station patrol boxes, as well as with the commandant's office, the other officials, and with the main telephone exchange connected with the switchboard in station No. 1.
With the 50-circuit board in station No. 1 were connected by direct wire 47 patrol boxes. Forty patrol boxes were connected with the 50-circuit board in station No. 2, and 26 with the 30-circuit board in station No. 3. All lines were run with rubber-covered, braided and twisted Hazard wire. In the central part of the grounds all wires were placed in conduits, most of which, it is said, were filled with water the entire season.
In giving the regular reporting signal, the receiver is taken from the hook, thus throwing the drop on the central-office switchboard, which corresponds with the number of the box with which it is connected. When the signal is received, the operator presses the listening key corresponding in number, and the guard reports his name and number, of which the operator makes a record, as well as the time the report is given.
A hand generator is mounted in the box, with a crank projecting through the inner door. This generator is used as the emergency or wagon call, and, when operated, rings the bell on the switchboard, and the shutter between the gongs indicates the number of the box calling. The bells in the box immediately above the wagon-call generator, are for the answer-back signal, and are rung from the central office when a wagon call is received, to indicate to the officer that there is no trouble on the line, that the call has been received, and that the wagon is being sent.
Back of these bells is a pair of heavy compound ringers, with a pair of four-inch gongs, placed in the top of the box, which are used for the recall bells. The top of the box has an opening on each side for the emission of sound from the bell; these bells will ring only when the door is closed, being cut out by a spring key when the door is open. The recall bell is for calling the officers instantly to the box at any time from the central office. The recall bells on any of the boxes can be rung separately, or all in the entire district may be rung simultaneously. Immediately under the wagon-call generator is mounted a long-distance transmitter, with a mouthpiece projecting through the inner door.
The receiver hook is a special platinum-contact gravity switch, cutting out of the circuit the entire box, excepting the recall bell, when the receiver is on the hook. The emergency-call generator is provided with an automatic shunt, and cuts itself in when operated. The receiver is a strongly -built, double-pole, horseshoe-magnet, adjustable instrument, and is provided with a special weatherproof long-conductor cord.
The apparatus is mounted in a heavy cast-iron weatherproof protection box of neat design, well painted with weatherproof paint. All the main parts are mounted back of an inner door, excepting the receiver, which is provided with a weatherproof cord, thus enabling the system being used in rainy and wet weather without affecting its working parts.
Fig. 3 shows box 37 in district No. 1, at the entrance of the Temple of Music, where President McKinley was shot on September 6th, and from which box the ambulance was called. This box is located on the outside of the building at the south entrance, where it is the most convenient for emergency use, as well as for the regular reporting of the guards. All the boxes on the grounds were placed in the most convenient and prominent places, and it is stated that the system was one of the most important and satisfactory features for the protection of the exposition.