VOLCANIC ACTION AND THE MICROPHONE.

Lyttelton Times, Volume LI, Issue 5604, 10 February 1879, Page 5

VOLCANIC ACTION AND THE MICROPHONE.

A correspondent of a Home paper, writing from Borne on Nov. 29, says:—ln an article communicated by Professor do Bossi, of Borne, to the Sollettino J del Volcd&imo Italiano , we find an interesting account of some experiments with - the microphone and telephone combined, to determine how far these instruments will serve in the science of terreons meteorology; end the result seems to be highly satisfactory. In 1875, and therefore some yean before Mr Edison himself so much talked of, Professor Mo* cenigo, of Vicenza, published an account of an instrument of his invention, containing all the fundamental principles of the microphone ; but as he devoted himself chiefly to perfecting it with a view to its usefulness in his special branch of science, meteorology, the microphone was invented while he was still studying. Professor Bossi at ones saw the possible importance of the new invention, and, as in some experiments made at Vicenza, j the telephone emitted sounds efitila ! only be attributed to subterranean agitations, l he determined to make some further ex peri* ments himself in an underground observatory of his own at Bocca di Papa, situated on the Alban Hills, on the edge of the crater of an extinct volcano. A special microphone, capable of being attached firmly to the rocks so as to feel any motion there might be, was carried down with great care into the obser* vatory, and the professor sat anxiously by it until late into the night, waiting for tb« hour when all was at rest and silent, to catch any sounds that might issue from the telephone. He soon found that the mysterious sounds mentioned to him by his brother professor were not fanciful; and though uncertain vs to their causes, he was soon able to divide them into three classes, which he «dl« rumb* lings, musketry reports, and metallic or bell* like sounds. He also discovered that the sounds were periodical at intervals of an hour, or half an hour, or even smaller fractions. Meanwhile (he says) nature was favourable to scientific inquiry, for on one side Vesuvius was becoming active, on the other several slight shocks of earthqnake.were felt at Bocca di Papa; thus it happened that twice 1 was listening to the telephone, when slight shocks were felt, and I noticed then that they were Preceded and. accompanied by the sounds I avo described. This happened while Vesuvius was increasing in eruptive activity; and on the night of Sept 22, at the hour when the explosions of the volcano and its eruptive cone were most vigorous, my microphone on the Latian hills was in the greatest agitation. On the following days the same sounds continued, following more or less exactly the course of the eruption of Vesuvius. Winning, however, to complete my evidence, I determined to cany my microphone to a place where there was no doubt of being on ground vibrating from inner causes—to the side of Vesuvius and the Solfatara of PozzuolL Professor Palmier! not only put at my disposal his observatory, but did all in his power to make the experiment a fair one, himself watching at the outer door to prevent all intrusion or accidental noises. We wished here to establish the connection between the motions of the seismograph and the sounds communicated by the microphone. To ascertain this, one of the assistants of the observatory stood over the seismograph, to mark the motions with signs previously agreed on, to record the agitation preceding a shock, the actual shock itself, and whether the motion was undulatory or perpendicular. At the same time the sounds of the telephone were noted, and found to correspond exactly with the motions of the seismograph; and each different motion corresponded to a different sound. In this way it was possible to ascertain the value of the different sounds, which had naturally been impossible at Bocca di Papa; and it appeared that the perpendicular motion corresponded to the musketry reports, and the undulatory to the rumblings; while very often there was an uncertain sound, as had been noticed at Bocca di Papa. It appears, too, that the microphone, when placed on ground continually agitated, works with great energy, even when not accurately adjusted, and this became ■till more evident when taken to the Solfatara of PozzuoU. Here, indeed, I expected greater results than on Vesuvius, as the area of eruption is more confined, and it was more easy to approach the centre of activity; and I was not disappointed; for the microphone, before being adjusted, when artificial vibrations had no effect on it, repeated violently the shocks and rumblings at the bottom of the enter. When the balance had been slightly adjusted tie reports became so loud that there was no necessity lor holding one’s ear to (he telephone, and it was quite sufficient to place it on a table for every one present to hear the sounds. Learning that I was about to repeat the experiment, many people came to assist, and all, but chiefly the ladies, could not repress a feeling of fear at hearing the force, rapidity, and variety of the sounds, which showed what a terrible furnace we were standing over. The most interesting part to me, however, was that there was no difference, except in intensity, between these sounds and those heard at Vesuvius and Bocca di Papa; and it was hence evident they all proceeded from volcanic sources. But while Our ears were filled with these noises there was no sensible motion experienced, as I had also remarked on Vesuvius, and, except in the two moments of earthquake, at Bocca di Papa. Still it is evident that the microphone both at Vesuvius and the Solfatara was registering shocks of earthquake otherwise imperceptible; and, os the same sounds had been observed by Professor Mooenigo at Vioensa and Ansellina at Borne, there can be no longer any doubt of tiie existence of mroroseismio vibrations of the earth as discovered by Bertelll and maintained by me. In other experiment* I have found it sufficient to place an ordinary watch under a nail and pass the electric current through this simple medium to catch the seismic sounds. The first - thing then that science requires in the application of the microphone ■to meteorology is to obtain an instrument which will marie automatically all the variety of sounds which the microphone conveys to us; and this will bo the much desired ■. * panseismograph,' which will show the number, form, and every variety of the vibrations of the earth." I have giyeh this account as far as possible in the learned -professor’s own words; but it ii necessarily only a summary of his paper, find leaves unnoticed many of his experiments and discoveries!