2oS 



NATURE 



[December 27, 1894 



motion from nest to east. Ano'.her paper on the sam e subject 

 is contributed to ihe BuIUUn by S. K^s'.insky. In this case, 

 tbe obierva'ions discu«ed were made with the greit meridian 

 iastrument of the Pullcova O >serva!or)', mounted in the prime 

 vertical. The period obtained was 411 days, and tli; amplitude 

 o "541. In addition to these patters, there is one on the orbits 

 of Bielid meteors, dedaced by M. Bredichia fron o bsetvations 

 made in 1892. 



ON A REMARKABLE EARTHQUAKE DIS- 

 TURBANCE OBSERVED ATSTRASSBURG, 

 MCOLAIEW, AND BIRMINGHAM, ON 

 JUNE 3, 1S93. 



Introductory Note. 



'pHE Horizontal Pemiiilum. — The observations described in 

 the subjoined article were made with the horizontal 

 pendalam desij^ned by Prof. Zoilner, and modified by 

 Dr. von Rebeur-Paschwitz. This instrument consists 

 of three thin brass tubes jointed together in the form of 

 an isosceles triangle, the vertical angle of which is about 

 45'. The two equal sides are prolonged slightly beyond 

 the base, and to the ends are attached two small spherical agate 

 cups, the concavity of the lower one being directed from the 

 centre of gravity "f the pendulum, and that of the upper one 

 towards it. When the pendulum is placed in position, these 

 cups rest on two steel-points attached to the stand of the 

 instrument and directed normally to the surfaces of the agate 

 cups. One steel-point is almost exactly above the other, so 

 that the axis of rotation is nearly, but not quite, vertical, its 

 inclination to the vertical being still great compared with the 

 movements of the ground we wish to investigate. The 

 pendulum rests in the vertical plane passing through the axis 

 of rotation, and on the side towards which it inclines. If this 

 is towards the east, and if the axis is slightly tilted in the 

 east and west plane, there will be no deflection of the 

 pendulum ; the only change will be in its sensitiveness. But if 

 the axis is lilted in any other plane, it will no longer incline 

 towards the east, and the pendulum will be deflected from its 

 original position, in order to remain in the same vertical plane 

 with the axis of rotation. It is evident that the smaller the 

 original inclination of the axis to the vertical, the greater will 

 be the deflection for a given tilt of the axis in the north and south 

 plane ; that is, the greater will be the sensitiveness of the 

 pendulum. 



From the middle of the nearly vertical tube of the pendulum, 

 there projects outwards a small bar. Passing through an 

 aperture in the frame to which the steel-points are attached, 

 this bar carries a mirror, whose plane is at right angles to that 

 of the pendulum. A ray of light, proceeding from a fixed source, 

 is reflected by the mirror, and registers the movements of the 

 pendulum on a strip of photographic paper wrapped round 

 a revolving drum. The zero-line is traced by a ray of light 

 reflected by a fixed mirror just below the other, and attached to 

 the stand of the instrument.' 



Obsenation of Earlhijualu Pulsations. — Nothing could show 

 l)etler than Dr. von Rebeur-I'aschwitz's interesting paper how 

 desirable it would be to have a few well-chosen stations in 

 different parts of the world where these pulsations could be 

 registered. They might then be traced .is they spread out from 

 the origin of a great earthquake, and might even be followed, 

 as he suggests, in their course, completely round the world. 



In several Italian observatories there are established instru- 

 ments suitable for this purpose. Horizontal pendulums, with 

 reording apparatus, are now at vtork at Charkow and Nicolaicw 

 in the south of Russia ; and two others will soon be ready at 

 Strassburg and Mcrseburg in Germany. A bifilar pendulum ■ 

 at Birmingham, belonging to the British Association, will 

 shortly be furnished with a photographic recorder. Thus 

 Europe is at present fairly well provided for. 



.\ large number of stations in other parts of the world is by 

 no means absolutely nccestary. Results of great value would 

 lie derived if recording instruments were erected at places near 



t For A fu'l'-r ..• ^(iinl of iVi* tiori/.nlrit p'n<liil-im. \ft Dr. von Kcbeur- 

 P.n- (' r'a Acta Her kail. 



/.. ', Bd. Ix. 1899, 



PI' ' ' 



■' NATUi;!^ Uu'y 'J. 1-/4). vjI. ;'j, w- -4' 4/ . Urii. Assoc. R«p,, j8<)3, 



pp. 29I.JO> 



NO. 1313, VOL. 51] 



the east aud west coasts of North America, in South .America, 

 South .\frica, India, Australia or New Zealand, and the Sand- 

 wich Islands. In Japan Prof. Milne's tromometer' leaves lit'le 

 to be desired. 



The chief element to be determined is the exact epoch of 

 the beginning, maximum amplitude, and end of the 

 pulsations, or of each group of pulsations. The hori- 

 zontal pendulum. Dr. von Rebeur-Paschwitz informs me, 

 can be arranged so that its sensitiveness for slow tilts of 

 the ground can be diminished without necessarily lessening its 

 sensitiveness for earthquake shocks. The strip of photo- 

 graphic paper can thus be reduced in width without running 

 any risk of the spot of light leaving the paper during its 

 ordinary daily and other movements. Without increasing the 

 expense, a more rapid movement of the paper could be per- 

 mitteil, and this would enable the determination of the time to 

 be made with greater accuracy. Possibly, also, the construc- 

 tion of the instruments might be simplified if earthquake- 

 pulsations arc to be the principal subject of investigation. In 

 the bifilar pendulum, for example, since the amplitude of the 

 oscillations is a point of minor importance, the somewhat 

 elaborate machinery for determining the angular value of the 

 scale divisions might be dispensed with, and also the arrange- 

 ments for readjusting the spot of light from a distance. 



Hardly less important in these investigations is the deter- 

 mination of the exact time of occurrence of the earthquake at or 

 near its centre of disturbance. But on this it is the less neces- 

 sary to insist, for in so many of the more marked seismic districts 

 there now exist organisations for the study of earthquakes. It 

 may not be out of place, however, to suggest that in all seismic 

 record-, and in every part if periodically published, the standard 

 time employed should be clearly stated. It is not universally 

 known, for instance, that, in Japan, Tokio time w.as replaced on 

 January i, 1SS8, by the time of 135° V.. long. In accounts from 

 Beluchislan, again, we cannot be certain whether Madras time 

 or railway time is meant, for both are used. The trouble of 

 inserting this important detail is hardly to be compared with 

 the confusion and error that may result from its omission. 



C. Davison. 



In the last report of the Earth Tremor Committee of the 

 British Association, reference is made to an observation of 

 earth-pulsations by Mr. C. D.ivison on the evening of June 3, 

 1S93, .It Birmingham, which was obtained liy the aid of Mr. 

 H. Darwin's bifilar pendulum. I take the following details 

 from the report : — .\t 5.43 p.m. (G.M.T.) the image was found 

 to be perfectly steady, liut .".t 6.29, when the observer returned 

 to the cellar, it was moving slowly and steadily from side to side 

 of the field of view, thus indicating the passage of a system of 

 earth-waves. At 6.42 the image had come to rest, but at 6.46 

 theoscill.ations commenced again, and continued to be visible with 

 varying amplitude until 8.13. After 8.13, though the observer 

 watched for two hours and a half, no further m ition was noticed. 

 The period of the waves was found by a number of observations 

 to be between fifteen and twenty seconds, and the range of 

 motion at its maximum one-eighth of a second. 



Mr. Davison's observation is especially interesting, because it 

 corresponds exactly with a :erj' , wtraori/inary <iistiiy/'<iiit<- which 

 was registered by the horizontal pendulumsat Strassburg and Nico- 

 laiew. Amongst the considerable number ol disturbances com- 

 mon to both these places, that o( June 3 is certainly the most pro- 

 minent during the interval from January I to September 4. 1893. 

 In the accompanying illustration (Kig. I) the two curves, obtained 

 by photography, are shown side by side ; in correspondence with 

 the difference of longitude between the two places, the lower 

 curve wa-s moved I7'5 mm. to the left. The pendulum in both 

 cases was placed in the east-west plane. In the fnllowing notes 

 the time is Greenwich'Mean Solar Time, and is given in decimal 

 parts of the hour. 



(a) .Slrasibiirg. — The disturbance begins suddenly and small 

 at 442, the curve having been perfectly sharp and steady before. 

 The range of motion increases to 4 mm. at 4 52 and decreases 

 at 469. It then again increases so as to make the curve dis- 

 appear entirely between 477 and 505. During the interval 

 the light-|)oint w.as displaced by 3^. mm. to the north, which 

 corresponds with a deflection of the pendulum towards the 

 south. At 482, the |)erson who keeps control over the instru- 

 ment entered the cellar, to look after it and to determine the 

 time correction, which is done by shutting off the light during 



' Brit. Assoc. Rep., 1899, pp. 107.109. 



