Nothing can be more remarkable than this power of listening to conversation while seated in an armchair six or seven yards from the instrument, nor is it necessary to move in order to reply. The correspondent, indeed, must be close to the acoustic tube in order to speak and listen, and he must speak rather loud in order to be heard at any distance from the other station. But the listener receives the sounds so amplified that it might be supposed that a giant was speaking, and conversation held in a low tone may even be distinguished. These results are really extraordinary, and even to those familiar with such effects this incessant progress is surprising. These results may be ascribed to the following causes:-- 1. First, that the conditions of the magnet are better than those of ordinary instruments. 2. That the diaphragm is also thicker, larger, and better stretched. 3. That the box is of metal, and calculated to act as a sounding-box. 4. The speaking trumpet magnifies the sounds. 5. The acoustic tubes concentrate the sound waves on the centre of the diaphragm. _Note on some fresh Experiments with Telephones without any Diaphragm._ In a paper published March 4, 1878, I made some suggestions on the theory of the sounds produced in the telephone, and on the contradictory assertions of physicists as to the transmission of speech by ordinary telephones when devoid of diaphragm. These remarks induced M. Ader to undertake some experiments which not only demonstrate the truth of my opinion, but bring to light some fresh facts which may be of great importance to acoustic science. M. Ader has in fact not only succeeded in making a telephone without a diaphragm speak, but he has made it speak more loudly and with less alteration of the voice than we find to be the case with a small model of the ordinary telephone. No one, therefore, can now maintain that the sounds produced by the magnetic cores are so faint that they cannot be taken into account among the effects produced, and that it is at any rate impossible for them to reproduce articulate sounds. To obtain this result, M. Ader reduced the size of the magnetic core to that of a simple iron wire, one millimètre in diameter, and he fastened it by one of its ends to a small wooden board. Under these conditions, it was enough to fasten a small helix of fine wire on this iron wire, and to apply the board to the ear in order to hear speech distinctly, with the aid of a microphonic speaker actuated by a voltaic current. But the range of sound was considerably increased if a mass of metal was applied to the free end of the iron wire: in this case it was possible to hear when the wooden board was removed to a distance of ten or fifteen centimètres from the ear.