Scientific American Supplement, July 2, 1892, pages 13758-13759:

Figure 1
    Of all the inventions with which we have been endowed by that marvelous fairy that we name electricity, there is none that has found so many applications as the telephone. The papers are constantly making known some new use of it, and as surfeited as we are at this end of a century that has witnessed so beautiful discoveries, the mind remains confounded before the progress made with an apparatus of which the name not longer than thirty years ago caused scientists to shrug their shoulders, and brought a smile to the countenance even of the most convinced believers in the omnipotence of electricity, without speaking of the use of the telephone in the army, where, as experience has many times demonstrated, it renders inestimable services during maneuvers, and will prove no less useful in the field. We now see in the United States, in several very extensive parishes, that the faithful for whom it would be impossible to go to the temple can, thanks to the telephone, follow the celebration of the offices without leaving the house. Moreover, at the Birmingham Hospital, the friends or relatives of the sick correspond with them, by telephone, and this permits of getting news from them directly without running any risk of infection. Further, the firemen now carry with them an apparatus by means of which, on their arrival at a fire, they can put themselves in communication with the central station and ask for the necessary help. Very recently, an inventor has proposed on analogous system that would permit trains remaining in distress between two stations to instantly make known the situation to the neighboring station. We shall speak, as a remembrancer only, of the services rendered by the telephone in the government departments, railway stations, etc., and of the numerous applications that it has found in medicine and surgery. The space reserved for this article would not suffice for the complete enumeration of such uses.
    Our object at present is to present to our readers one of the most recent innovations founded upon the use of the telephone, viz., the theatrophone, the installation of which in Paris, scarcely two years old, has, in this short interval of time, taken a development which is very remarkable. Every one knows these little apparatus (Fig. 4) which are now to be found in the large hotels, cafes, restaurants, theater vestibules, etc., which proceed both from the telephone and the automatic distributer, and which, through the introduction of a 50 centime piece into a slot, permit of listening for five minutes to a morceau that is being played upon the stage of a theater and the title of which is given in a wicket in front of the apparatus. During the listening, if an intermission occurs, the name of the first theater is replaced by another, and the auditor is immediately put in communication with another stage. If an intermission occurs at a given moment in all the theaters, the apparatus will allow a piano or a song to be heard, so that in no case will the auditor run the risk of giving his money for nothing.
    This result is obtained as follows: The central station of the Theatrophone Company (Fig. 1) is connected with secondary stations placed in the theaters. Each of these secondary stations is provided with batteries, bobbins, call apparatus, commutators, etc., and communicates with a series of microphones placed upon the stage on each side of the prompter's box. The cables that connect these stations with the central station end at a distributing board to which are likewise fixed the cables that run to the theatrophone and a certain number that run to the central telephone office of the Opera Avenue. The role of these latter will shortly be explained. Figure 2
    The cables of the theatrophone are formed of three conductors; two of these twisted together serve for the transmission of the music, and the third actuates the alarm. The same cable serves for several apparatus. Thus, to mention but one example, the line of the Continental Hotel serves a total of twelve apparatus distributed between the Rhine, Dominici, London, Continental, St. James, Albion, Windsor, Wagram and Brighton Hotels. The apparatus are not necessarily fixed. It suffices to arrange collectors along the line of the cable and to connect these with the apparatus when it is desired to make them operate. Such is the case with the Café de la Paix, which has four movable apparatus and sixty collectors. When the apparatus is stationary, the signaling is easily effected by means of the third conductor, as we have said. In the case of movable apparatus it is impossible to operate in the same way. Fixed alarms, independent of the theatrophone, are then arranged at certain definite points and well in view. The theatrophone is provided with a button, which permits of re-establishing the synchronism between its indications and those of the fixed alarms controlled by the central station.
    At present the company has installed in Paris 100 apparatus, grouped upon eleven different lines.
    But, aside from the theatrophone service, the company has also a certain number of subscribers, that is to say private individuals, who, through the payment of a fixed amount, have the right to a certain number of listenings at home. It is to this service that is devoted the third group of cables that end at the distributing board already mentioned. These persons are necessarily subscribers also of the telephone. It follows that, in order to allow them to use the theatrophone, the operator of the Opera office will merely have to connect the subscriber's line with the one coming from the central station of the theatrophone whose number is indicated by the operator of this latter station. Figure 3
    After passing into the distributing board, all the cables end at a switch board, which does not differ sensibly from those used by the administration of telephones. However, as the number of lines to be served here is not so large, it has been possible to give the spring jacks a rectangular form and to adopt much larger movable plugs having the advantage that all their parts are metallic externally, thus greatly facilitating surveillance and repairs. Fig. 2 represents one of these plugs.
    Referring to the switch board, it will be seen that the operator has at her right, within reach of her hand, a crank that serves to operate the alarms of the various lines of the theatrophones. A repeating telegraph placed at the top of the board, and through which passes the third wire of the cable, indicates the alarm has operated properly. By reason of the somewhat large size of the card board disk that carries the names of the various theaters (Fig. 3), the inventors have been led to adopt for the mechanism of the alarm the arrangement shown in the same figure. Owing to the stop seen to the left, each revolution of the crank causes the ratchet wheel supporting the disk to advance by one tooth only. The motion is therefore rendered sufficiently slow to prevent the disk acting like a flywheel and skipping several divisions at a time.
    The small levers placed to the right of the board serve, some of them, for sending the current into the circuits of the theatrophones and others into the subscribers' lines. The operator having introduced a plug with flexible cord into the spring jack corresponding to the Opera, for example, and the other extremity into the jack carrying the number of the subscriber whom it is desired to connect with this theater, has only to depress the lever of this same number in order to establish a communication. As each theater cable is formed of six double conductors all ending at the board, it follows that it is possible to connect the same theater with several lines at once. A telephone permits the operator to turn at every instant to the theater line and verify the operation. If she discovers any irregularity, she at once notifies the theater. Finally, every subscriber's cable, on leaving the switch board, passes into a commutator, which permits of sending the current into a measuring apparatus and of thus verifying the resistance of the line as often as may be desired. Such is the installation that very recently permitted the Lord Mayor of London to give some guests an opportunity of listening to the opera, and the prefect of Nantes to hear the latest popular songs without having to submit himself to the smoky atmosphere of a concert hall. Let us hope that the theatrophone will soon be completed by the theatrophote, and that the eye will be able to follow the actors at the same time that the ear hears their words.--Les Inventions Nouvelles.
Figure 4