The experiments on the microphone made in London at the meeting of the Society of Telegraphic Engineers on May 25, 1878, were wonderfully successful, and they were the subject of an interesting article in the ‘Engineer’ of May 31, which asserts that the whole assembly heard the microphone speak, and that its voice was very like that of the phonograph. When the meeting was informed that these words had been uttered at some distance from the microphone, the Duke of Argyll, who was present, while admiring the important discovery, could not help exclaiming that this invention might have terrible consequences, since, for instance, if one of Professor Hughes’s instruments were placed in the room in Downing Street, in which Her Majesty’s ministers hold their cabinet council, their secrets might be heard in the room in which the present meeting took place. He added that if one of these little instruments were in the pocket of Count Schouvaloff, or of Lord Salisbury, we should at once be in possession of the secrets for which all Europe was anxiously waiting. If these instruments were able to repeat all the conversations held in the room in which they stood, they might be really dangerous, and the Duke thought that Professor Hughes, who had invented such a splendid yet perilous instrument, ought next to seek an antidote for his discovery. Dr. Lyon Playfair, again, thought that the microphone ought to be applied to the aërophone, so that by placing these instruments in the two Houses of Parliament, the speeches of great orators might be heard by the whole population within five or six square miles.

The experiments lately made with the microphone at Halifax show that the Duke of Argyll’s predictions were fully justified. It seems that a microphone was placed on a pulpit-desk in a church in Halifax, and connected by a wire about two miles long with a telephone placed close to the bed of a sick person, who was able to hear the prayers, the chanting, and the sermon. This fact was communicated to me by Mr. Hughes, who heard it from a trustworthy source, and it is said that seven patients have subscribed for the expense of an arrangement by which they may hear the church services at Halifax without fatigue.

The microphone has also lately been applied to the transmission of a whole opera, as we learn from the following account in the ‘Journal Télégraphique,’ Berne, July 25, 1878:—

‘A curious micro-telephonic experiment took place on June 19 at Bellinzona, Switzerland. A travelling company of Italian singers was to perform Donizetti’s opera, “Don Pasquale,” at the theatre of that town. M. Patocchi, a telegraphic engineer, took the opportunity of making experiments on the combined effects of Hughes’s carbon microphone as the sending instrument, and Bell’s telephone as the receiver. With this object he placed a Hughes microphone in a box on the first tier, close to the stage, and connected it by two wires, from one to half a millimètre in thickness, to four Bell receivers, which were placed in a billiard-room above the vestibule of the theatre, and inaccessible to sounds within the theatre itself. A small battery of two cells, of the ordinary type used in the Swiss telegraphic service, was inserted in the circuit, close to the Hughes microphone.

‘The result was completely successful. The telephones exactly reproduced, with wonderful purity and distinctness, the instrumental music of the orchestra, as well as the voices of the singers. Several people declared that they did not lose a note of either, that the words were heard perfectly; the airs were reproduced in a natural key, with every variation, whether piano or forte, and several amateurs assured M. Patocchi that by listening to the telephone they were able to estimate the musical beauty, the quality of the singers’ voices, and the general effect of the piece, as completely as if they had been among the audience within the theatre.

‘The result was the same when resistances equivalent to 10 kilomètres were introduced into the circuit, without increasing the number of cells in the battery. We believe that this is the first experiment of the kind which has been made in Europe, at least in a theatre, and with a complete opera; and those who are acquainted with the delicacy and grace of the airs in “Don Pasquale” will be able to appreciate the sensitiveness of the combined instruments invented by Hughes and Bell, which do not suffer the most delicate touches of this music to be lost.’

Although experiments with the microphone are of such recent date, they have been very various, and among other curious experiments we learn from the English newspapers that the attempt has been made to construct an instrument on the same principle as the telephone, which shall be sensitive to the variations of light. It is known that some substances, and particularly selenium, are electrically affected by light, that is, that their conductivity varies considerably with the greater or less amount of light which is shed upon them. If, therefore, a circuit in which a substance of this nature is inserted, is abruptly subjected to a somewhat intense light, the increase of resistance which results from it ought to produce a powerful sound in a telephone inserted in the circuit. This fact has been verified by experiment, and Mr. Willoughby Smith infers from it, as we have already suggested, that the effects produced in the microphone are due to variations of resistance in the circuit, which are produced by more or less close contacts between imperfect conductors.

In order to obtain this effect under the most favourable conditions, Mr. Siemens employs two electrodes, consisting of network of very fine platinum wire, fitting into each other like two forks, of which the prongs are interlaced. These electrodes are inserted between two glass plates, and a drop of selenium, dropped in the centre of the two pieces of network, connects them on a circular surface large enough to establish sufficient conductivity in the circuit. It is on this flattened drop that the ray of light must be projected.