In the very earliest days of the telephone, music played at Philadelphia was transmitted, by means of Elisha Gray's musical telephone , to New York. Similar applications have since frequently been made, and amongst them may be mentioned some which attracted a good deal of attention at the time. We refer to the repetition of theatrical performances during the Paris Exhibition of 1881. The performances at the Opera, Opera Comique, and Theatre Francais could be distinctly heard in a room of the Exhibition building set apart for this purpose. Not only the voices of the actors and actresses, the songs and the orchestra, but all the incidents of the performance-the applause and laughter of the audience, and, in some cases, the voice of the prompter, too-were faithfully repeated, and listened to with intense pleasure by a never-tiring crowd of visitors. The following was the arrangement for the telephonic repetition of the performance at the Opera :-

The conducting wires led from the Exhibition through the sewers to the stage of the Opera, where they were connected to a number of Ader transmitters, with multiple contacts... There were 10 transmitters of this kind at the Opera, which were placed on either side of the prompter's box, along the footlights. The receivers placed in the telephone rooms of the Exhibition were Ader's telephones, and the installation of the batteries for the working of these multiple systems had nothing peculiar about it.

They were placed wherever there was room for them, generally below the stage; but as polarisation would take place to a serious extent if their circuit remained closed during a whole performance, they had to be changed every quarter of an hour, and a switch had to be so arranged as to effect these changes instantaneously. This switch consisted of a board provided with as many spring plates as there were transmitters, and which allowed the switching on or off the batteries working the microphones.

The greatest difficulty which had to be encountered was to render the transmitter more sensitive to the voices of the singers than to the predominating sounds of the orchestra. This difficulty was overcome by M.Ader by the following contrivance:-

Let us suppose two microphonic transmitters placed on the stage at T and T' (Fig. 282), and these transmitters separately connected by two distinct wires to two telephonic receivers, R and R', which are applied to both ears to hear the actor, whom we will suppose to be placed at A. It is easy to understand that, the distance of this actor from transmitter T being less than that from transmitter T', his song will be more distinctly reproduced by transmitter T than by T', and the stronger impression will be produced on the left ear. If, on the contrary, the singer changes his position to A 1 , the opposite result will be obtained, and the right ear will receive the stronger impression. The sensation produced will, therefore, be a change of sonorous intensity from one ear to the other, consequent upon the displacement of the sound or of the singer from right to left, and the same will be the case for several actors crossing one another on the stage.

Now, we have mentioned that on each side of the prompter's box, along the footlights, five transmitters had been installed. Each of these transmitters had its separate circuit, and consequently its underground cable.

On arrival at the audience room, each of the cables was connected to eight receivers, but always in such a way that for each listener the effects were quite distinct for each ear. Fig. 283 shows the arrangement of circuits for two transmitters, and it will be similar for all the others. It will be seen, on reference to Fig. 283, that on each board of the telephone room there was always one telephone, that on the left, which corresponded to the transmitters on the left of the stage, and a telephone on the right, which corresponded to the transmitters on the right.

The telephones of each section were connected in series. These telephonic repetitions have since been frequently repeated, not only at the Electrical Exhibitions of Munich and Vienna, but also in London, where the United Telephone Company have frequently conveyed Sullivan and Gilbert's operas to the Royal Society, and to several other places.

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