i8o 



NATURE 



\yune 19, 1879 



paper ribbon. The length of paper corresponding to an 

 hour of time being known, it is easy to determine the in- 

 stant at which the mark has been made, viz., the instant 

 at which the shock has occurred. 



Without any doubt the most interesting article in last 

 year's Bulletino is that on the application of the micro- 

 phone to the study of subterraneous meteorology, by 

 Prof. Michele de Rossi. In 1875 Count C. Mocenigo, of 

 Vicenza, made an observation which was nothing less than 

 the fundamental fact of the microphone, at a time when 

 neither microphone, phonograph, nor micro-tasimeter 

 had been invented. He observed that electric cunents 

 indicate perturbations and interruptions in a galvano- 

 meter by means of frictions and shocks produced arti- 

 ficially between conductors not in perfect contact (" per 

 effetto soltaiito di attriti e di scosse communicate artifi- 

 cialmente ai conduttori posti fra loro in semplice con- 

 tatto instabile " ). He also observed that the same pheno- 

 mena were produced by natural and unknown causes, 

 when the apparatus had not received any artificial shock.' 

 The account which he gave of his observations led 

 Prof, de Rossi to conclude that these unknown per- 

 turbations arose from microseismic oscillations of the 

 soil. He communicated his views to Count Mocenigo, 

 wto at once commenced to make experiments in the 

 direction indicated, in the midst of which the news of 

 the invention of the microphone in America, was received. 

 Prof, de Rossi at once endeavoured to apply it to the de- 

 tection of subterranean phenomena, and for this purpose 

 he commenced a series of experiments in the seismic 

 observatory which he has established at Rocca di Papa, 

 one of the Alban Hills about seventeen miles from Rome. 

 A special microphone consisting of a balanced pointed 

 lever lightly touching a plate of silver, was mounted on a 

 stone pedestal, and was placed twenty metres under- 

 ground, at a distance from habitations and from roads. 

 It was also thoroughly isolated and shut up in a box filled 

 with wool. The instrument was watched during some of 

 the stillest hours of the night, and the same mysterious 

 sounds which Count Mocenigo had recognised were heard 

 by de Rossi, which he considers were incontestably natural 

 and intra-telluric. The sounds were carefully analysed, 

 and were compared with artificially produced sounds. 

 The microseismic sounds were speedily differentiated 

 from other sounds, and their nature was completely con- 

 firmed when it was observed that they were often coinci- 

 dent with movements of the seismograph, and that they 

 were of a periodic character. On one occasion, as de 

 Rossi was listening at about half-past three o'clock in the 

 morning the telephone connected with his subterranean 

 microphone emitted sounds like the discharge of mus- 

 ketry, of such loudness that he feared they would awaken 

 a child who slept in the same room, and he therefore dis- 

 connected the telephone. A short time afterwards, 

 towards four o'clock, a sensible shock of earthquake 

 occurred, for which the sounds had been the microphonic 

 preparation. 



In the beginning of last September Vesuvius showed 

 many signs of an approaching eruption. During the 

 night of the 22nd of that month the mountain produced 

 thundering sounds, and at the same time loud metallic 

 noises were heard in the microphone, more than a hundred 

 miles distant. The microphone was soon afterwards 

 transported to the observatory on Vesuvius, and it was 

 then possible to trace the precise correspondence between 

 the movements of the seismographs and the sounds of the 

 microphone, and moreover to ascertain the seismic value 

 (il significato sismico) of the different sounds of the micro- 

 phone. It was also ascertained that if a watch were 

 connected with the microphone, the noise of the tic-tac 

 heard in the telephone became much louder just before a 

 shock, and gradually less and less loud as the seismic 



** Fen'jmtn'i singolarl di interferenza fra le correnti elettriche ed i promossi 

 mecanicamente sul legno." — Bassano, 1875. 



agitation died away. This led Prof, de Rossi to impro- 

 vise a microphone which he has found very useful for 

 microseismic purposes. 



A watch, A, is placed upon a suitable stand, and a thin 

 copper wire, B, connected with the positive pole of a small 

 battery is arranged, as shown in the figure, so that one 

 end of it, furnished with a steel needle, rests lightly upon 

 the smooth silver surface of the watch. The handle of 

 the watch is connected by the wire with the telephone, 

 the other binding screw of which is connected with the 

 negative pole of the battery. Such an arrangement fur- 

 nishes a very effective microphone, if the degree of con- 

 tact between the needle and the surface of the watch be 

 carefully regulated. G. F. Rodwell 



OUR ASTRONOMICAL COLUMN 



The Occultation of Antares, July 28. — The only 

 occultation of a very conspicuous star during the present 

 year which is visible in this country and in fact the only 

 one higher than the second magnitude up to the year 

 1883, is that of Antares on the evening of July 28. It 

 will take place at a low altitude here. As is well known 

 Antares is a double star, and the effect of the duplicity 

 was shown by observation of the occultation of the star 

 by the moon, before the companion was detected by 

 Mitchel at Cincinnati in July, 1845. The appearance of 

 a comparatively faint star at emersion, suddenly brighten- 

 ing up to the full brilliancy of Antares, had been recorded, 

 and a suspicion of duplicity entertained at least in one 

 instance, some twenty years previous. Interest therefore 

 attaches to the occultation of July 28, and with the view 

 to facilitate the determination of the times of immersion 

 or emersion at any place in this country, we will apply 

 the Littrow-Woolhouse method of distributing the predic- 

 tion of the phenomenon. Direct calculations give the 

 following results for Greenwich, Edinburgh, and Dublin ; 

 the moon's place is corrected nearly to agree with 

 Newcomb's theory : — 



From which, putting the latitude of the place = 50° + l 

 (l in degrees), and the longitude in minutes of time = M 

 (-f if east, - if west of Greenwich), we find- - 



h. m. 

 G.M.T. of Immersion = 9 36-86 + 0-84I L + 0-263 M 

 „ Emersion = 10 10-74 - 2-507 L + 0*462 M 



Angle from N. Point at Immersion = 149*4 + 2*6 L - 0*1 M 

 ,, ,, Emersion = 204*2 - 2*7 L + 0*2 M 



These formulae give for — 



Which are Greenwich mean times : the angles are 

 reckoned as is usual in the occultation-predictions of the 

 Nautical Almanac, for the inverted image. At Greenwich 



