502 



SCIENTIFIC NEWS. 



[Nov. 16, 



below, whilst Mr. J. Bell, C.E., drew the plans, and Mr. 

 C. T. Vachell, M.D., looked after the business and legal 

 matters. Owing to the joint exertions of these gentle- 

 men on the occasion of our visit in September, things 

 had assumed the stage of advance indicated in the fol- 

 lowing plan ; the dotted lines show the course of the 

 trench, whilst the various points of interest are num- 

 bered and duly indicated : — 



1. First dry stone wall. 12. Remains of old woman. 



2. Second „ ,, 13. Hypocaust. 



3. Stone and mortar wall. 14. Second enclosure : room with 



4. Urn of black pottery. tesselated floor. 



5. Part of bronze fibula. 15. Grave with human (female) 



6. First enclosure. remains. 



7. Part of quern. 16. Impression of horse's hoof. 



8. Large portion of pillar. 17. Another room. 



9. Fragment of pillar with base. 18. Graves with human remains. 



10. Finial. 19. Rectangular solid founda- 



11. Coins. tion. 



(To be continued.) 



THE PREVISION OF EARTHQUAKES. 



UNDOUBTEDLY the attempts at foretelling destruc- 

 tive natural phenomena, such as tempests, floods, 

 or earthquakes, meet with very general attention, but do 

 not as a rule encounter either the confidence or the dis 

 trust which they merit. Hence it is required, in the 

 interests of true science, that specialists — unpleasant as 

 the task may prove — should undertake an examination 

 of the data and the assumptions upon which such prophe- 

 cies are founded. With especial reference to the last 

 great earthquake in the Riviera, on February 23rd, 1887, 

 Professor Hein takes occasion to undertake, in the 

 Naturforscher, a thorough-going exposition of the notorious 

 earthquake predictions of Falb. 



At present geology distinguishes three kinds of earth- 

 quakes : — Collapse earthquakes, due to the subsidence of 

 subterranean caverns, and felt over a very narrow space, 

 are but of slight importance. Volcanic earthquakes are 

 usually the forerunners of eruptions, and are, therefore, 

 limited to volcanic territories. They never extend over 

 wide regions, but the number of shocks is often very 

 considerable. The dislocatory or tectonic earthquakes are 

 the most common and the most important. Though 

 without any direct connection with volcanoes, they 

 agitate extended regions of the earth's surface, and take 

 place along certain zones or lines of previously-existing 

 displacements of the strata. Where such shocks are 

 numerous, they occasion permanent displacements of the 

 surface, which are even capable of measurement. As an 

 example may serve, the triangular region Lagern — Rigi 

 — Napf, in which the first-named point has moved nearer 

 to the two latter by a metre (39 inches) in the course of 

 the last thirty years. 



Some time ago A. Perry, of Dijon, collected statistical 

 evidence on earthquakes, and considered himself entitled 

 to assert that these catastrophes occurred more frequently 

 at new and full moon than at other times. This led him 

 to the hypothesis of a tidal movement in the liquid inte- 

 rior of the globe, earthquakes being thus due to the 

 action of a spring-tide. Though Perry himself subse- 

 quently ceased to advocate his hypothesis, it found a 

 champion in Rudolf Falb, who considers all earthquakes 

 as subterranean volcanic outbreaks occasioned by the 

 attraction of the sun and the moon. 



The only evidence advanced by Falb in support of his 

 theory was of a statistical character, and this he does in 

 a manner open to objections. Thus he ignores the great 



earthquake of Villach in 1348, which was unfavourable 

 to his hypothesis. He also assumes that the earth- 

 quakes may occur from three to five days earlier or 

 later, though the total interval between the times of their 

 supposed maximum and minimum occurrence is only 

 seven days. The same convenient liberty, we may 

 remark, is claimed by those meteorologists who expect 

 a change in the weather at the quarters of the lunation. 

 Further, since systematic observations of earthquakes 

 have been collected, they have been found almost ot 

 daily occurrence. In the year 1880 fifty-nine shocks were 

 experienced in Switzerland, and in the following year 166. 

 From August 1st, 1870 to August rst, 1873, there occurred 

 in the Greek province Phokos 300 destructive shocks and 

 50,000 slight agitations. We may therefore assume, 

 with a great probability, that in his earthquake statistics 

 Falb has scarcely taken into consideration a thousandth 

 part of the earthquakes which have occurred during the 

 same time. 



A discussion of the recent statistics of earthquakes 

 shows in some groups no connection with the position 

 of the moon. In other series there appears an excess 

 of a few per cents, at full and new moon, as against the 

 intermediate quarters. From the great frequency of 

 earthquakes there can be found not merely slight but 

 severe shocks, which agrees with Falb's supposition. But 

 the same statistics show plainly that the moon is not the 

 primary, nor even the secondary, cause of earthquakes. 

 Its influence is restricted to facilitating by a small 

 percentage the release of the tensions produced by other 

 causes in the crust of the earth at the times of spring- 

 tide. 



Falb exaggerates the action of the tides of the earth's 

 nucleus in another direction. The solid crust of the 

 earth, he admits, is plastic enough to yield to a 

 tidal wave of, at the outside, a foot in height, and to 

 accommodate its form accordingly. This is evident, as 

 the solid matter passes downwards into the liquid state, 

 not abruptly, but by intermediate stages of a plastic 

 character. Further, on Falb's hypothesis, the subter- 

 ranean earthquakes must be the most common, and the 

 shocks must proceed from a central point — both of which 

 points are very rarely experienced. Lastly, the pre- 

 diction of further shocks in a district which has been 

 visited by destructive agitations is no particular proof of 

 acuteness. It has long been known that every somewhat 

 severe earthquake is heralded by some faint, often 

 scarcely perceptible, shocks. Then comes the main con- 

 vulsion as a group of shocks in rapid succession, followed 

 for months or years by great agitation, until the disturbed 

 strata have come to an equilibrium, and the threatening 

 tensions in the regions concerned have entirely or 

 chiefly disappeared. And these tensions in the earth's 

 crust depend not on a tendency to subterranean outbreaks, 

 but upon the subsidence of the crust upon a contracting 

 nucleus. 



The Mirage again. — According to Cosmos, a most 

 remarkable case of mirage was seen at St. Maurice 

 (Valais) on October nth last. There was seen — 

 evidently in the night, though the exact hour is not 

 given — the image of a splendid cathedral as if projected 

 on a white cloud. Buttresses, bell-turrets, and the 

 tower, with its lofty steeple, were all seen by several 

 spectators during at least half an hour. Supposing that 

 there is no exaggeration in the description, we have here 

 a problem no less difficult than interesting. 



