In addition to the disturbing causes in telephonic transmission we have just mentioned, there are others which are also very appreciable, and among them are the accidental currents which are continually produced on telegraphic lines. These currents may proceed from several causes, at one time from atmospheric electricity, at another from terrestrial magnetism, at another from thermo-electric effects produced upon the lines, at another from the hydro-electric reactions produced on the wires and disks in communication with the earth. These currents are always very unstable, and consequently they are likely, by reacting on the transmitted currents, to modify them so as to produce sounds upon the telephone. Mr. Preece asserts that the sound proceeding from earth currents somewhat resembles that of falling water. The discharges of atmospheric electricity, even when the storm is remote, produce a sound which varies with the nature of the discharge. When it is diffused and the clap takes place near at hand, Dr. Channing, of Providence, U.S., says that the sound resembles that produced by a drop of fused metal when it falls into water, or, still more, that of a rocket discharged at a distance: in this case it might seem that the sound would be heard before the appearance of the flash, which clearly shows that the electric discharges of the atmosphere only take place in consequence of an electric disturbance in the air. Mr. Preece adds that a wailing sound is sometimes heard, which has been compared to that of a young bird, and which must proceed from the induced currents which terrestrial magnetism produces in the metallic wires when placed in vibration by currents of air. M. Gressier, in a communication made to the Académie des Sciences on May 6, 1878, has spoken of some of these sounds, but he is totally mistaken in the source to which he ascribes them. ‘In addition to the crackling sound caused by the working of telegraph instruments on the adjacent lines, a confused murmur takes place in the telephone, a friction so intense that it might sometimes be thought that the vibrating disk was splitting. This murmur is heard more by night than by day, and is sometimes intolerable, since it becomes impossible to understand the telephone, although nothing is going on in the office to disturb the sound. The same noise is heard when only one telephone is used. A good galvanometer inserted in the circuit reveals the presence of sensible currents, sometimes in one direction, sometimes in another.’