March 4, 1909J 



NA rURE 



echelon, so that the band of Assuring followed the 

 general run of the movement in the underlying rock. 

 Following on the description of the surface move- 

 ments along' this rift, and the account of the re- 

 triansulation of the country on either side of it, is a 

 detailed description of the distribution of the violence of 

 shock, and discussion of the course of the isoseismals. 



These have a peculiar distribution ; the maximum vio- 

 lence was along a narrow band closely adjacent to the 

 rift line, where surface displacements were greatest, 

 but the progressive diminution of violence, as this 

 line is left, is interrupted by a number of isolated 

 areas of destructive violence. In 

 discussing the explanation of these 

 isolated centres of increased vio- 

 lence, the conclusion is reached 

 that they are due to variations in 

 the nature of the ground, and to 

 be attributed to the well-known 

 fact, illustrated by some interesting 

 experiments contained in the 

 report, that earthquakes are com- 

 monly more destructive on allu- 

 vium or made ground than on rock ; 

 but in atteiTipting to ascribe all 

 the irregularities in the course of 

 the isoseismals to this cause, we 

 cannot but feel that the committee, 

 or, rather, its chairman, has 

 given its support to an obsolescent 

 theory. So many instances are 

 now known of extended origins, 

 and of earthquakes with more 

 than one centre of maximum vio- 

 lence, that an attempt to refer an 

 earthquake to a single centre of 

 origin is no longer justifiable 

 unless this hypothesis is easily 

 reconcilable with observation. In 

 this case it seems more reasonable 

 to accept the isolated centres of destruction, or of in- 

 creased violence, as independent centres of origin of 

 the same great earthquake, not of separate local earth- 

 qu.ikes, as suggested and controverted in the report. 



NO. 2053, '^'OL. 80] 



The experiments, to which reference has been made, 

 are of great interest, and throw light on some little 

 understood earthquake phenomena. They were made 

 with a shaking table, set in motion by a crank and 

 connecting-rod, of the same type as that employed 

 in the Japanese experiments on the overturn of 

 columns ; the table carried a box which was filled 

 with sand or gravel, dry, or mixed 

 with different proportions of water, 

 a[id determinations were made of 

 the amplitude and character of 

 movement of the surface of the 

 sand as compared with that of the 

 table. U'ith closely packed dry 

 sand there was little difference, but 

 with wet sand the amplitude was 

 greater, and, what is more im- 

 portant, the reversal of motion 

 much more abrupt, giving an 

 acceleration which, in one experi- 

 ment, was more than three times 

 as great as that of the table. We 

 have here a suggestion of the 

 reason for this fact, which has 

 often been observed, that the de- 

 structive effect of an earthquake 

 is greater on alluvium near its 

 junction with rock than on the 

 rocks or further out on the 

 alluvium, and it is to be hoped 

 that this very interesting and sug- 

 gestive line of experiment may be 

 followed up more fully than was 

 possible in time for the publica- 

 tion of the report. 

 Only a few of the more striking 

 features of this report have been referred to; it would 

 be impossible to deal in detail with the discussion on 

 scales of intensity, the direction of vibratory move- 

 ment, the effect of the shock on men and animals, 

 and the many other matters described with a pro- 



-I'omlsalonL; Rift n. 



lixity of detail, and " exprest " in a language 

 which, with thankfulness be it said, has not yet 

 become " thrlv " unintelligible to the average 

 Englishman. 



