I30 



NATURE 



\May 30, 1878 



brushing is insufficient to produce sound, still they may 

 move the charcoal sufficiently to produce alternations of 

 current, each of which may be able to set up vibrations 

 in the telephone plate in its own period, or a modification 

 of it, giving what I call the jarring sound. If, therefore, 

 we have this sound, we know that either the microphone 

 is exposed to sounds so loud as to produce complete 

 break of contact, or that there is a motion going on 

 affecting it, of insufficient rapidity to be audible. 



With the object of reproducing the voice or musical 

 notes, I have made the following modification of the instru- 

 ment : — A ferrotype plate 3 inches in diameter is fastened 

 over a hole z\ inches in diameter in a thick piece of wood ; 

 a flat piece of gas carbon weighing a few grains and 

 having a fine copper wire attached to it is fastened to the 

 top of the plate in the centre ; over the piece of carbon is 

 suspended by a wire spring another piece of carbon finely 

 pointed, weighing about \ oz , and adjusted so as just to 

 touch the carbon plate. The current is then led by the 

 wires through the carbon point, and by careful adjustment 

 of the latter almost any degree of sensitiveness can be 

 attained. Whenever the sound becomes too loud the 

 current is broken, and minute sparks are seen at the 

 carbon point, and the jarring sound is heard at thd same 

 time in the telephone. The sound of a musical box is 

 perfectly reproduced when the box is held in the air ; the 

 instrument is therefore sensible to sound-waves in air as 

 in solids. Geo. M. Seabroke 



Rugby 



I SEND an account of an experiment with the micro- 

 phone which may interest some of your readers. 



A microphone, made of three pieces of gas carbon (as 

 described by Prof. Hughes) and the primary wire of a 

 Du Bois Reymond's induction-coil, are placed in the 

 circuit of a single Daniell cell. The Avires from the 

 secondary coil (pushed home) are attached to the poles 

 of a Lippmann's capillary electrometer. The Daniell 

 and microphone are twenty-five feet distant from the 

 electrometer. If an observer watches the capillary- 

 tube and speaks or sings to the microphone {which is 

 twenty-Jive feet distant) definite and large movements of 

 the mercury-column will be seen. The movements for 

 various letters resemble those which have been pre- 

 viously observed to take place with the telephone, the 

 "w" giving its curious double movement. 



F. J. M. Page 



Physiological Laboratory, University College, 

 London 



EARTHQUAKE IN VENEZUELA 



T N the evening of the 12th of this month a severe earth- 

 ■■■ quake destroyed the town of Cua, in this country. Cua 

 is situated on the left bank of the River Tuy, in 10° 8' 15" 

 L. N. and 66° 55' W., Green w. The height over the level 

 of the Caribbean Sea I found in 1873, by barometrical 

 measurement, 232 metres. It was the centre of a very 

 flourishing agricultural district (annual produce, about 

 80,000/. a year), and had about 3,000 inhabitants. 



The weather had been for weeks exceedingly hot, as 

 generally this year in Venezuela. At 5 o'clock in the 

 afternoon, before the earthquake, a temperature of 100° 

 is said to have been noticed, and six days later, at the 

 same hour, I observed myself 95°. The sky was clear, 

 and the moon in perfect brightness. The shock occurred 

 some minutes before a quarter to nine o'clock, and so 

 violent was it that in less than two seconds all the centre 

 of the town was a heap of ruins. It is impossible to fix 

 the exact time of the shock, but it was felt in Cardcas at 

 8h. 41m. 34s., the distance in a straight line between both 

 places being about twenty-six English miles. 



The centre of the town was situated on a small hill, 

 about 20 metres over the lower part. The hill is com- 



posed of gneiss, micaceous and chloritic schists, rising 

 rather steep towards W.S.W. This hill is surrounded by 

 strata of clay and marl, covered by a deep stratum of 

 alluvial soil, and resting on dark limestone and argil- 

 laceous schists, containing numerous crystals of iron 

 pyrites. 



Only the upper town was laid waste ; the lower part 

 suffered comparatively very little. From actual observa- 

 tions I found that the angle of emergence of the shock 

 was about 60°. The centre cannot have been very deep, 

 as the destruction was limited to a spot measuring only 

 one square mile, although the shock of the transverse 

 wave was felt in places 100 miles distant. The soil had 

 burst at different places, giving issue to water highly im- 

 pregnated with sulphuretted hydrogen. The shocks con- 

 tinued for several days, and are not yet entirely gone, but 

 no further damage has been caused. About 300 people 

 were killed ; the loss of property is said to be about 

 300,000/. sterling. 



I have reason to think that this earthquake had nothing 

 to do with volcanic forces, but was due to an interior sub- 

 sidence or downfall of calcareous rock, as I intend to 

 prove in a special memoir on this subject, as soon as I 

 shall have visited the locality once more. 



Caracas, April 30 A. Ernst 



OUR ASTRONOMICAL COLUMN 



Tempel's Comet, 1873, II. — We continue the ephe- 

 meris of this comet, for the latter half of June, as given 

 by M. Schulhof in the Paris Bulletin International of 

 May 7. If the calculated epoch of perihelion passage 

 be approximately correct, the intensity of light will be 

 increasing, and the comet would arrive at its least 

 distance from the earth early in July. But the possible 

 error in the mean motion determined from the observa- 

 tions of 1873, may render a search over a wide extent of 

 sky unavoidable, if the comet is to be recovered at the 

 present return. Shortly before the completion of his 

 calculations M. Schulhof informed the writer that the 

 probable error in the mean daily motion would not exceed 

 ± 7", but this degree of uncertainty involves a difference 

 of nearly ± 20 days in the date of perihelion passage, so 

 that the comet may be found after close search in a 

 position considerably distant from the computed one. As 

 in other similar cases, if the observer has the command 

 of an equatorially-mounted instrument of good aperture, 

 the most promising plan of search will be to commence 

 at the calculated declination for the day, extending the 

 sweep to 30m. or 40m. on each side of the calculated 

 R.A., and to continue the same proceeding for 3° or 4° on 

 each side of the calculated declination. It may be re- 

 marked that the computed R.A. for a certain change in 

 perihelion passage, varies more rapidly than the com- 

 puted declination. Perhaps there is a greater proba- 

 bility of the comet being detected at the latter end of 

 June than subsequently, if the weather is generally 

 favourable for a careful search. 



The following positions for Paris midnight are deduced 

 on the assumption that the comet will arrive at perihelion 

 Sept. 1*5, the most probable date : — 



T,- T,., » • N. Declina- Distance from Intensity 



Right Ascension. j;^„_ ^^^^ of light, 



h. m. s. , / 



June 15 ... 15 34 44 ... 5 6 ... 0-667 ... 0-90 



„ 19 ... IS 32 15 ... 4 17 ... 0-659 ••• o'9S 



„ 23 ... 15 30 20 ... 3 20 ... 0-654 ••• o"99 



„ 27 ... 15 29 5 ... 2 15 ... 0-651 ... 1-05 



July I ... 15 28 31 ... I I ... 0-649 ... 1-06 



The RECENT Transit of Mercury.— In the instruc- 

 tions for observing this phenomenon suggested by 

 Prof. Newcomb, and circulated by the United States 

 Naval Observatory, it is remarked that "its accurate 

 observation is of especial importance as affording data 



