NATURE 



97 



THE SHIVERING EARTH. 

 Seismology. By John Milne, F.R.S., F.G.S. Pp. xvi 

 + 320. (London : Kegan Paul, Trench, Triibner, and 

 Co., Ltd.) 



PROFESSOR MILNE spent more than twenty years 

 in Japan. When he went there he was experienced 

 IS a miner and geologist ; and had spent years in New- 

 Ifoundland, Iceland, Arabia, Siberia and Mongolia as an 

 explorer. He was Professor of mining and geology, and 

 later, of seismology, but for twenty-three years he seems 

 to have devoted himself to the one subject, seismology. 

 The Transactions of the Seismologiral Society of Japan 

 are mainly of his writing. He has published books and 

 numerous papers in England. Through his influence the 

 Japanese Government has established many seismo- 

 logical observatories. He seems to have made a thorough 

 trial of hundreds of seismometers. He enlisted the 

 observational services of many of the foreigners living 

 in Japan. As Secretary of the British Association Com- 

 biiittec he has written numerous valuable reports. He 

 !has induced all the engineers and architects in Japan to 

 build in accordance with the conclusions drawn by him 

 ifrom his observations. During the last two years he has 

 ibeen the means of establishing twenty-three seismological 

 (Stations over the world, and he considers it his duty to 

 (keep in communication with them all. 

 ' In all these years he seems to have missed no chance 

 of supplementing his own mathematical and scientific 

 knowledge by that of anybody whom he could induce to 

 study his subject. He has a pleasant style, and knows 

 |from experience as a popular lecturer exactly how his 

 jsubject may be made interesting to the general reader, 

 and the result is a very readable book which probably 

 contains all that is worth knowing on this subject at the 

 present period of its development. Twenty such volumes 

 might have been written if the author had cared to touch 

 on all the crude speculation of quasi-scientific workers 

 which has from time to time been published. 



The earth, about whose interior we know as much as 

 Carlyle's ephemera knew about the lunar theory, is in- 

 tensely hot under enormous pressure at all depths below 

 a few miles. As the inside cools it contracts, and the 

 crust must also get smaller, and so we have all sorts of 

 crumpling and buckling actions going on slowly always ; 

 gradual changes of slope which show themselves mainly 

 by changes of sea level. A small vertical fall or rise in 

 water level may accompany enormously great changes in 

 land area. A lift of all the Tertiary mountainous dis- 

 tricts to an average height of 4000 feet would seem to 

 have required only a vertical fall of the water level of 

 twenty-six feet, although the actual breadth of land e.x- 

 posed at coasts may possibly have been very great ; and 

 by the possible repeated exposure and submergence of 

 great areas of sedimentary beds, accompanying the prob- 

 able discontinuous rise of the mountains. Prof. Milne 

 throws an unexpected light on the well-known fact that 

 the great mountain-forming epochs in geological history, 

 epochs of great brady-seismical and volcanic activity, 

 have a close chronological identity with the periods 

 NO. I 5 18, VOL. 59] 



of coal formation. That there has been crumpling 

 in the past is evident enough ; but it is interesting 

 to note how we are getting evidence that it is still going 

 on ; that the surface of the earth almost everywhere is 

 changing in slope, and falling and rising. Not only 

 have we tilting due to mere change of atmospheric pres- 

 sure ; to rain being better retained by some kinds of crops 

 than others ; to the attraction of the moon ; to the melt- 

 ing of polar ice ; to the erosion of land by sea and river ; 

 and the more or less continuous slipping of soil on steep 

 slopes, but to a far more important extent locally, by the 

 deposition of sediment at the mouths of rivers. Every 

 now and again the bending crust undergoes fracture, 

 especially at the bases of monoclines. Some kinds of 

 rock keep fracturing continually ; others yield without 

 fracture for long times, and when they fracture they do 

 it with violence ; faults are suddenly formed, possibly at 

 great depths, and the motion, the sudden shiver or 

 vibration is transmitted to every part of the earth. If 

 the fault occurs near the surface of the earth, other 

 evidence of it appears than the temporary passage of an 

 imperceptible or terrifying shiver ; in minor dislocations, 

 horizontal displacement and sometimes actual contraction. 

 Thus in Japan in the Neo valley in i8gi some plots of 

 ground were diminished 30 per cent, in breadth ; river 

 beds were permanently narrowed ; forests slipped down 

 from mountain sides to block up valleys and form great 

 lakes ; the whole land on one side of the valley lowered 

 in level, and a boundary ridge of high mountains with it. 

 Any one who looks at maps of the world published by 

 the Electric Cable Companies will notice how, along the 

 west side of -South America, and at many places else- 

 where, a cable is not brought along the coast directly from 

 one place to another ; for safety it goes out to sea a great 

 distance. If we did not have actual evidence of it, we 

 could not believe in the numerous sudden large changes 

 of sea bottom which occur, fracturing submarine cables. 

 Except in Japan no people are so enthusiastic in the 

 establishment of Prof Milne's observatories as those 

 interested in such cables. In 1888 the simultaneous 

 fractures of three submarine cables between Australia 

 and Java by an earthquake caused Australia to mobilise 

 its naval and military forces ; and on several occasions 

 Prof. Milne has been able to answer questions of the 

 Colonial Government as to the cause of fracture of 

 cables. 



The earthquake or shiver is transmitted to all parts 

 of the earth. The student of acoustics may imagine how 

 the complicated system of vibration gets reflected and 

 refracted and changed in character as it travels, and how 

 different the complete record must be at a place near to 

 the primary disturbance from what it is six thousand 

 miles away, and how anywhere it depends on the local 

 character of the ground. And yet, in spite of this com- 

 plication, there are interesting general rules which have 

 been derived by the author from observation. A dis- 

 turbance which has travelled 6000 miles, is recorded by 

 preliminary simple tremors which may have periods of 

 5 to 12 seconds, the more decided movements having 

 periods of from 20 to 40 seconds. At places nearer, the 

 motion is more complicated ; the preliminary tremors 

 have periods of from '04 to '2 sec. ; the decided move- 

 ments, say with ranges of motion 10 to 20 mm., have 



