If this double electro-magnetic system is inserted in a line circuit, it follows that, for each discharge of the transmitted current, a corresponding attraction of the branches of the tuning-fork will take place, and consequently there will be a vibration, producing a sound, if the discharges are numerous. This sound will naturally be short or long in proportion to the duration of the sender’s action, and it will be the same as that of the tuning-fork in that instrument. Again, if one branch of the tuning-fork reacts on a contact P inserted in the circuit of the local battery communicating with a Morse receiver, traces will be produced on this receiver of length varying with the duration of the sounds, for the Morse electro-magnet will be so quickly affected by the successive breaks in the current that its armature will remain stationary throughout each vibration. ‘I have not yet been able,’ said M. Lacour in an address delivered before the Danish Academy of Science in 1875, ‘to calculate the time necessary for the production of definite vibrations in the tuning-fork. Different factors have to be considered, but experiment has shown that the time which elapses before the local circuit is broken is such a small fraction of a second as to be almost inappreciable, even when the current is very weak. ‘Since intermittent currents only affect a tuning-fork on condition that it vibrates in unison with the one which produces them, it follows that if a series of sending tuning-forks, tuned to the different notes of the scale, is placed at one end of a circuit, and if a similar series of electro-magnetic tuning-forks, in exact accordance with the first, is placed at the other end of the circuit, the intermittent currents transmitted by the sending tuning-forks will be added to each other without becoming confused, and each of the receiving tuning-forks will only be affected by the currents emitted by the tuning-fork in unison with it. In this way the combinations of elementary signals representing a word may be telegraphed simultaneously.’