A different arrangement of the microphone is required for the transmission and the reproduction of speech by this system, and a section of the one which Mr. Hughes found most successful is given in fig. 45. It somewhat resembles Mr. Hughes’s microphone speaker, placed in a vertical position, and the fixed carbon is fastened to the centre of the stretched membrane of a string telephone. The ear or mouth tube is at A, the membrane at D D, the carbon just mentioned at C: this carbon is of metallised charcoal prepared from deal, and so also is the double carbon E, which is in contact with it and is fastened to the upper end of the little bar G I. The whole is enclosed in a small box, and the pressure exerted on the contact of the two carbons is regulated by a spring R and a screw H. The tube of the telephone serves as an acoustic tube for the listener, and Mr. Hughes’s speaker, described above, acts as sender. It is hardly necessary to say that the two instruments are placed at each end of the circuit, that the carbons are connected with the two poles of a battery of one or two cells of bichromate of potash, or two Bunsen or six Leclanché cells, and the two instruments are connected by the line wire. Under such conditions, conversation may be exchanged, but the sounds are always much less distinct than they are in a telephone. I was able to ascertain this fact with a roughly made instrument brought from England by Mr. Hughes. MM. Berjot, Chardin, and de Méritens, who were also present at the experiments, were able with me to hear speech perfectly, and I have since successfully repeated the experiment alone, but it does not always succeed, and under its present conditions the instrument has no importance in a scientific point of view. It is evident that the instrument can dispense with any support, and the little box then forms the handle of the instrument; in this case the two binding screws are placed at the end of this handle, as in a telephone. The microphone speaker with a disk, represented in fig. 5, which acts as sender to the singing condenser, can be used, when properly regulated, as a receiving microphone. M. Berjot has obtained good results from a little instrument of the same kind as that in fig. 45, but with a metal diaphragm, and the microphonic system consists of a cylindrical piece of carbon resting on a small disk of the same substance, which is galvanised and soldered to the diaphragm. The whole is enclosed in a small round box, with its upper part cut in the form of a mouthpiece. It seems that all microphone senders with disks can reproduce speech more or less perfectly; it is a question of adjusting and refining the carbon points of contact. A weak battery, consisting of a single Leclanché cell, is better for these instruments than a strong battery, precisely because of the effects of oxidation and polarisation, which are so energetically produced at these points of contact when the battery is strong.