An induction coil is necessarily employed for a long circuit, and the effects of induction in the adjacent wires are modified by two rheostats introduced into the circuit at its two extremities. _Further remarks on the theory of the Telephone._--Following the example of a certain sceptic in the Académie des Sciences, Colonel Navez continues to maintain the theory first formed as to the mode in which the telephone acts, in spite of the clearest proofs of its insufficiency; but most scientific men who consider the question have come round to our opinion, and admit the concurrence of several causes in the reproduction of speech by this remarkable instrument. Mr. Fleeming Jenkin writes to this effect in the new edition of a treatise on Electricity and Magnetism. He observes that a singular fact has been discovered by several persons, who have ascertained that not merely non-magnetic and non-conducting bodies can be substituted for the diaphragms of receiving telephones, but that they will act without a diaphragm at all. In this case it is evident that we have to do with the sounds discovered by Page, and that they are produced by the magnet itself, in which each molecular movement constitutes the source of the sound produced. This sound becomes articulate as soon as its increase and decrease can follow the increasing or decreasing action of the voice which produces it at the sending station. It is certain that when the transmitted currents are due to the action of the Bell diaphragm, the sounds due to the Page effects ought to correspond with those which would be given by iron diaphragms adapted to the receiving instruments; so that, when a telephone has an iron diaphragm, there are in fact two voices, that of the diaphragm, which is strong, and that of the magnet, which is weak. When a disk of wood is substituted for one of iron, it acts as a sounding board for the Page effect, and when the disk is of metal, induction is developed by the magnetic modifications, and tends to produce vibration, thus developing a third source of sound, which may be called the Ampère effect. Finally, a fourth source of sound may result from the induced effects produced in the wire itself in consequence of changes in the intensity of current. These sounds, first observed by M. de la Rive, have since been studied by Mr. Fergusson of Edinburgh (vide ‘Telegraphic Journal’ of November 1, 1878).