DE J 'EL OP ME NT OF SETSMOL OGY IN JAPAN 301 



by Terada'^'^ who was not able to detect any magnetic disturbance 

 indisputably connected witli an earthquake. Eapid i)ulsatory variations 

 of the magnetic field were mostly not local phenomena, but probably 

 of atmospheric origin. It is greatly to be regretted, however, that 

 observations at Aburatubo had been suspended early, and no record of 

 this sensitive magnetogi-aph could be obtained on the occasion of the 

 last great earthquake, of which the origin Avas situated very near the 

 station. 



On the other hand, tlie investigation of the geographical dis- 

 tribution of the terrestrial magnetic elements has been considered 

 important, especially because Tanakadate and Nagaoka*^-^ found a 

 remarkable change in the isomagnetics of the Mino-Owari district after 

 the destructive earthquake of 1891. A general magnetic survey of 

 Japan was planned and carrit^d out by Tanakadate under the auspices 

 of the E.l.C^^^ The field work was conducted by a number of parties 

 of observers consisting chiefly of Students and Graduates in Physics, of 

 Tokyo Imperial University, among whom we find the names of the 

 prominent physicists of tlie present days. The results of the survey 

 were thoroughly examined and discussed by Tanakadate and published 

 as Vol. 14 (1904) of the Journal of the College of Science,^^^ in which 

 the formulae as well as the charts for the different elements, all 

 reduced to 1895.0, are given. Charts of the distribution of magnetic 

 disturbances there appended will be of much interest for future 

 seismologists and geophysicists. 



The second general magnetic survey was undertaken by the 

 authority of the Naval Hydrographic Office, during the interval from 

 April 1912 to May 1913, with the collaboration of Messrs. Tanakadate, 

 N. Watanabe and Tokuro Nakano. The results are published as Vol. 

 2 (1918) of the Bulletin of the Hydrographic Office, I.J.N./^^ in which 

 the data are all reduced to 1913.0 and the formulae and tables for 

 secular variations and accelerations for extrapolation are adduced. 



Foi' the above survey works, the set of magnetometers was designed 

 and improved and the methods of observations and reduction were 



(1) Journ. Coll. Sci. Tok., 37, Art. 9 (1917); T.S.BK., 8 (1916), 566. 



(2) Journ. Coll. Sci. Tok-, 5 (1893), 149. 



(3) See for the earlier survey : C.G. Knott and A. Tanakadate, Journ. Coll. Sci. 

 Tok., 2(1889). 



(4) Also, T.S.B.K., 2 (1904), 149; 2 (1905), 405; 8 (1915), 122. 



(5) A resume by T. Nukano, T.S.B.K,, 8 (1915), 126. 



