DE VEL OP MEN! ' OF SEISMOL OGY IN JAPAN 2^1 



tides instead of assuming simple ideal tides, as was done in the 

 previous undertakings. His results*^^^ thus obtained are interesting from 

 seismological as well as from geophysical points of view by showing 

 a reliable measure of the actual deformation of the crust caused by 

 the water load applied along the coast. 



Later, E. Sekiguti^-^ investigated a similar problem at Jinsen, 

 Korea, where the tidal range is abnormally large, amounting to 35 ft. 

 in the extreme case. From the records of an ordinary Omori horizont- 

 al pendulum seismograph, he succeeded in sorting out tlie tilting of 

 the earth crust due to tidal loading and obtained a value for the 

 rigidity of the crust which is in good agreement with that obtained 

 by Shida at Kamigamo. It must be remarked that in these investiga- 

 tions Nagaoka's theory of the elastic deformation due to surface loading, 

 already cited, has been of gi'eat aid in tbe analytical parts of the 

 work. 



Since the recent great earthquake, the need has been keenly felt 

 of some means which may serve for continuously watching the crustal 

 movement, as it may be reasonably expected to give some sensible 

 predictory symptom previous to a catastrophic fracture of the crust. 

 While the use of Michelson's instrument was being much spoken of, 

 an ingenious simple apparatus meeting the need was devised by T. 

 Shimizu.-''^ It consists essentially of a water tube, of which the free 

 surfaces at both (,nds are read by means of micrometers. The uni- 

 formity of the temperature of the water is insured by circulating it 

 through the pipe by the action of a pump. Though the apparatus is 

 ap2'arent]y simplicity itself, he has succeeded in attaining with it an 

 accuracy of 0.1 mm. /km., by carefully avoiding sources of possible 

 errors, an accuiacy which seems quite sufficient for most pur^joses here 

 concerned. 



On the other hand, D. Nukiyama^''^ chose a still simpler wa}- of 

 using the ordinary sensitive spirit level of an astronomical instrument 

 for his investigation of the tilting of the crust on the coast of Mera, 

 Awa, where the tidal effect could be expected to be considerable. 

 Besides, the place was near that part of Sagami Bay where the origin 

 of the recent great earthquake is believed to have been situated. 



(1) Mera. Kyo., 4 (1912), 1 ; T.S.B.K., 6 (1912). 2-12, 273. 



(2) Mera. Imp. Mar Obs., 1 (1917), 1. 



(3) Jap. J. Astr. Geoplivs., 2 (1924), 67; N.S.B.K., [iii] 6 (1924\ 54. 



(4) Not yet, lut to be shortly, published. 



