TELEPHONIC PERTURBATIONS.

Daily Telegraph (Napier), Issue 3204, 5 October 1881, Page 4

TELEPHONIC PERTURBATIONS.

The peculiar noifes which perturb the vocal messages on a telephone line have been made the subject of investigation by M. Gaiffe, the well-known French electrician, and, curiously enough, he finds them to be due to the vibrations and oscillation of the iron telegraph wires in the wind. These extraneous sounds have hitherto been referred entirely to the inductive action of neighbouring telegraph lines over which currents of electricity wer. passing ; though this cause is doubtless opeiative, it i 3 not the only one. M. Gaiffe arranged a telephone line along the floor of his laboratory and connected it by flexible conductors to the telephones at either end. a n interrupter, or key, was connected in circuit so that the circuit might be broken without disturbing the rest of the apparatus ; and he soon found that the mere rubbing of the line wire against itself generated a current which could be distinctly heard in the telephones when the circuit, was bi'oken by the key Rubbing another metnl on the line wire also produced a distinct effect, and even the friction of a binding screw upon the latter produced an audible sound, while scratching the line wire along a file gave a comparatively loud result. It follows that the rubbing of a telephone line against a seww or loose binding wire will occasion currents capable of perturbing a telephone message, and that well-soldered joints and a carefully ordered line are necessary for good telephony. A more serious drawback exists, however, in currents

generated by the virbrations of the wive itself, as M. Gaiffe has proved by inserting a rod of iron about 4ffc long in the circuit of the telephones and striking it transversely with a hammer. Every blow produced audible sounds in the telephones, although the flexible connection of the latter prevented a mechanical communication of the vibrations. This effect i 8 evidently a molecular one, and reminds us of the late experiments of Professor Hughos on electrical torsion, where the slightest torsion of an iron wire was found to alter its electrical condition, and conversely the pas.»ngp of a current. through the wire was demonstrated to produce a molecular twi.it in the latter. The vibration produced by the wind in tp]"pbonp Hops are therefore *"m":::it-ill to lonff-diatjiwe t<»h»phony, end the q'icstii'm arises how in obviate the difficulty. Underground lines a'-e, of courae, frep from any such ntmoephpric disturbance, but a« they tire similar in to submarine cables, their great inductive capacity would prove a more serious bar to telephonic speech, and a hundred miles or les? would probably render the telephones absolutely silent. ASrial wires of brass, or, better still, of manganese bronze, would perhaps solrff the difficulty.— Rngineering.

Hour.