200 



SCIENCE. 



[Vol. V., No. 109. 



the velocity given to the strip of photographic paper. 

 Of course, as seismometers, they would be as worthless 

 as all stable pendulums must be; but as seismoscopes, 

 they might be quite sensitive, and the expense and 

 requisite attention need not add greatly to that al- 

 ready necessary with the magnetometer. 



In Japan, Professor Milne keeps up his active work 

 in seismology. During the last summer, he spent 

 five days on the top of Fujiyama, attempting to detect 

 diurnal changes in the level of the ground. The re- 

 sults have not yet been published. This mountain — 

 a wonderfully symmetrica] volcanic cone, about twelve 

 thousand feet high, and the most striking object in 

 all Japan — is the one on whose summit Professor 

 Mendenhall made a determination of the force of 

 gravity and of the values of the magnetic elements ; 

 and it will always be an interesting point for scien- 

 tific observations of all kinds, rising as it does in 

 complete isolation out of a plain. 



In vol. vii. part 2, of the Transactions of the seis- 

 mological society of Japan, Professor Milne con- 

 tributes a paper upon three hundred and eighty-seven 

 earthquakes observed in northern Japan between 

 October, 1881, and October, 1883. A map is given 

 for every quake, showing by its colored portion the 

 approximate area covered by the shock, as determined 

 by Professor Milne's system of tracking down earth- 

 quakes by a system of postcards distributed to all 

 important places in the hands of observers who send 

 in weekly reports of the occurrence or non-occur- 

 rence of any disturbances. In this way Professor 

 Milne has had the northern part of Nippon and the 

 southern part of Yezo covered for several years with 

 a network of forty-five observers, besides those in 

 Tokio and Yokohama. At five of these stations 

 quite accurate time-observations of the disturbances 

 were frequently obtained by the help of good clocks 

 compared several times per week with the daily tele- 

 graphic noon signal from Tokio. A catalogue of the 

 individual observations of each of the three hundred 

 and eighty-seven shocks is also given. Some of the 

 results are worth noting. As regards geographical 

 distribution, it is remarkable that only two out of the 

 three hundred and eighty-seven shocks appear to have 

 extended to the west of the range of mountains 

 running up the western side of the island of Nippon, 

 being apparently stopped by that barrier, while about 

 eighty-four per cent seem to have originated either 

 out under the ocean or very near it on the eastern 

 side of the islands. Commenting on this, Professor 

 Milne says, — 



"The district which is most shaken is the flat al- 

 luvial plain of Musashi following the line of the river 

 Tonegawa. . . . This area forms one of the flattest 

 parts of Japan. The large number of earthquakes 

 which have been felt on the low ground, and the com- 

 paratively small number which have been felt in the 

 mountains, is certainly remarkable. 



" It must also be observed, that, in the immediate 

 vicinity of active or extremely recent volcanoes, the 

 seismic activity has been small. ... It may also be 

 remarked that the side of Japan on which earth- 

 quakes are the most frequent is the side which slopes 

 down steeply beneath an ocean which at a hundred 



and twenty miles from the coast has a depth of about 

 two thousand fathoms, whilst on the opposite side 

 of the country, at the same distance from the shore, 

 the depth is only about a hundred and forty fathoms. 

 Another point not to be overlooked is the fact that 

 the district where earthquakes are the most numerous 

 is one where there is abundant evidence of a recent 

 and rapid elevation. 



" In all these respects the seismic regions of Japan 

 hold a close relationship to similar regions in South 

 America, where we have earthquakes originating 

 beneath a deep ocean at the foot of a steep slope on 

 the upper parts of which there are numerous volcanic 

 vents, whilst, on the side of this ridge opposite the 

 ocean, earthquakes are rare. With regard to the 

 Musashi area, it may also be remarked that sediments 

 brought down by numerous rivers from the higher 

 parts of the country are accumulating on it at a very 

 rapid rate." 



The distribution of the three hundred and eighty- 

 seven earthquakes for the four quarters of the years 

 was as follows, — January -March, 195; April - June, 

 70 ; July - September, 39 ; October - December, 83, — 

 thus confirming the greatest activity in the coldest, 

 and least in the hottest, months of the year, which 

 had been shown before for the Tokio district alone 

 for a long period of years. 



With respect to the measurement of the motion of 

 the ground, most of the facts deduced by Professor 

 Milne are substantially the same as those summa- 

 rized by Professor Ewing in his memoir referred to 

 above. The following, however, which is partly, at 

 least, new, deserves quotation here: — 



" Inasmuch as it will be observed that different 

 instruments give different results for the same earth- 

 quake, in order that the reader may not regard such 

 diagrams as conflicting, the following results, which 

 have been obtained from the earthquakes here re- 

 ferred to, and which have been confirmed by many 

 observations made subsequently, may be enumer- 

 ated : 



"1. An ordinary earthquake, although having a 

 general direction of propagation, has at a given point 

 many directions of vibration. If there is a decided 

 shock in a disturbance, this particular movement 

 may be indicated in the same manner at adjacent 

 stations. 



"2. The amplitude of motion as observed at two 

 adjacent stations, even if only a few hundred feet 

 apart, may be extremely different. 



" 3. The period of motion may vary like the am- 

 plitude, the instruments being in all cases as similar 

 as it is possible to construct them. 



" At present I am carrying on observations by means 

 of three similar instruments placed at the corners of 

 a triangle the sides of which are about eight hundred 

 feet in length. When these instruments are side by 

 side, they practically give similar diagrams. At their 

 present positions, they always give different diagrams. 

 If these instruments were in the hands of distinct 

 observers, each of these observers would give a totally 

 different account of the same earthquake. Judging 

 from the quick period and large amplitude of mo- 

 tion always observed at one particular corner of my 

 triangle, I can say with confidence that at this corner 

 there might be sufficient motion to shatter a build- 

 ing, whilst at the other corners similar buildings 

 would not be damaged." 



