458 



NA TURE 



[March 13, 1884 



pendulums, and at every disturbance the movement of 

 one will predominate. From this Rossi argues that the 

 character of the microseismical motions is not constant. 



Bertelli observed that the direction of oscillation of the 

 pendulums is different at different places, but each place 

 will have its particular direction dependent upon the 

 direction of valleys and chains of mountains in the neigh- 

 bourhood. Rossi shows that the directions of movement 

 are perpendicular to the direction of lines of faults, the lips 

 of these fractures rising and falling, and producing two 

 sets of waves, one set parallel to the line of fracture and 

 tl e other perpendicular to such a direction. These move- 

 ments, according to Bertelli, have no connection with the 

 wind, rain, change of temperature, and atmospheric 

 electricity. 



The disturbances, as recorded at different towns, are 

 not always strictly synchronous, but succeed each other 

 at short intervals. If, however, we take monthly curves of 

 the disturbances as recorded at different towns in Italy, 

 ue see tliat these are similar in character. The maximum 

 disturbances occur about the winter solstice and the 

 minimum about the summer solstice, and in this respect 

 they show a perfect accordance with the curves drawn by 

 Mallet to show the periodicity of earthquakes. 



At Florence before a period of earthquakes there is an 

 increase in the amplitude and frequency of vertical move- 

 ments. The vertical movements do not appear to come 

 in with the horizontal barometrical disturbances, but they 

 appear to be connected with the seismic disturbances. 

 They are usually accompanied with noises in the tele- 

 phone, but as the microphone is so constructed aj to be 

 more sensitive to vertical motion than to horizontal mo- 

 tion, this is to be expected. This vertical motion would 

 appear to be a local action, inasmuch as the accompanying 

 motions of an earthquake which originates at a distance 

 are horizontal. Storms of microseismical motions appear 

 to travel from point to point. Sometimes a local earth- 

 quake is not noticed on the tromometer, whilst one which 

 occurs at a distance, although it may be small, is dis- 

 tinctly observed. To explain this, Bertelli suggests the 

 existence of points of interference and the existence of 

 nodes. 



Similar results were arrived at by Rossi when experi- 

 menting at diflerent points on the sides of Vesuvius. 

 Galli noticed an augmentation in microseismic activity 

 when the sun and moon are near the meridian. Grablovitz 

 found from Bertelli's observations a maximum two or 

 three days before the syzigies, and minimum three days 

 after these periods. He also found that the principal 

 large disturbances occurred in the middle of periods 

 separating the quadrature from the syzigies, the apogee 

 from perigee, and the solstice period from the nodes, 

 whilst the smallest disturbances happened in the middle 

 of periods opposed to these. 



P. C. Melzi says that the curves of microseismical 

 motions, earthquakes, lunar and solar motions, show a 

 concordance with each other. With the microphone 

 Rossi hears sounds which he describes as roarings, ex- 

 plosions, occurring isolated or in volleys, metalUc and 

 bell-like sounds, ticking, &c. , which he says revealed 

 n ttural telluric phenomena. These are sometimes in- 

 tolerably loud. At Vesuvius the vertical shocks corre- 

 sponded with a ?ound like volleys of musketry, whilst the 

 undulating shocks gave the roaring. Some of these 

 sounds could be imitated artificially by rubbing together 

 the ccnducting-wires in the same manner in which the 

 rocks must rub against each other at the time of an 

 earthquake, or by placing the tnicrophone on a vessel of 

 boiling water, or by putting it on a marble slab and 

 scratching and tapping the under side of it. 



These then are some of the more important results 

 which have been arrived at by the study of microseismic 

 motions. One point which seems worthy of attention is 



that they appear to be more law-abiding than their violent 

 relations, the earthquakes, and as phenomena in which 

 natural laws are to be traced they are certainly deserving 

 of our attention. As to whether they will ever become 

 the means of forewarning us against earthquakes is yet 

 problematical. Their systematic study, however, will 

 enable us to trace the progress of a microseismic storm 

 from point to point, and it is not impossible that we may 

 yet be enabled to foretell where the storm may reach its 

 climax as an earthquake. This, I believe, is a view held 

 by Prof de Rossi. 



Before the earthquake of San Remo, on December 6, 

 1874, Rossi's trcmometer was in a state of agitation, and 

 similar disturbances were observed at Livorno, Florence, 

 and Bologna. Since February, 1883, I have observed 

 a tromometer in Japan, and such results as have been 

 obtained accord with results obtained in Italy. 



The increase in microseismical activity with a fall of 

 the barometer is very marked. The style of the pendulum 

 does not always oscillate about the same point — there is 

 a deflection in the vertical. In Manila Father Faura also 

 makes observations with a tromometer, which I am told 

 gives him by movements very decided indications of 

 approaching typhoons. 



As to the cause of tromometric movements we have a 

 field for speculation. Possibly they may be due to slight 

 vibratory motions produced in the soil by the bending 

 and crackling of rocks produced by their rise upon the 

 relief of atmospheric pressure. If this were so, we should 

 expect similar movements to be produced at the time of 

 an increase of pressure. 



Rossi suggests that they may be the result of an in- 

 creased escape of vapour from molten materials beneath 

 the crust of the earth consequent upon a relief of external 

 pressure. The similarity of some of the sounds which 

 are heard with the microphone to those produced by 

 boiling water are suggestive of this, and Rossi quotes 

 instances w'hen underground noises like those which we 

 should expect to hear from a boiling fluid have been 

 heard before earthquakes without the aid of microphones. 

 One instance was that of Viduare, a prisoner in Lima, 

 who, two days before the shock, 1S24, repeatedly pre- 

 dicted the same in consequence of the noises he heard. 



A possible cause of disturbances of this order may be 

 the sudden fluctuations in barometric pressure which are 

 visible during a storm. 



In addition to the observations which have been 

 especially made for the purpose of recording earth 

 tremors, there are numerous observations which have 

 been made upon these disturbances when they have 

 appeared as intruders in investigations on other subjects. 

 .-\mongst these may be mentioned the endeavours to 

 measure changes in the vertical, as for instance those 

 which might be produced by the attractive influence of 

 the moon. 



Prof Zollner, who invented the horizontal pendulum, 

 found that the readings of his instrument were always 

 changing. 



M. d'.4bbadie, who for several years observed a 

 reflected image in a pool of mercury contained in a basin 

 of solid rock, found it a rare occurrence that the surface 

 of the mercury was tranquil. Sometimes it appeared to 

 be in violent motion. 



George and Horace Darwin, in their experiments at 

 Cambridge to determine the disturbing influence of 

 gravity by lunar attraction, found that the irregular 

 and persistent tremors in the ground, as indicated by the 

 instruments, were sufficient to mask whatever elfecls may 

 have been due to the influence of the moon. 



A full account of these latter observations is to be 

 found in Messrs. G. and H. Darwin's Report for 1882 to 

 the British Association. 



The general conclusion, then, is that from observations 

 in England, France, Germany, Italy, the Philippines, 



