JOURNAL OF THE COLLECrE OF SOIENOE TOKY'J IMPERIAL UNIVERSITY. 



VOL. XXXVII., ARTICLE 9. 



TO Professor Aikitu Tanakadate 



ON TUE OCCASION 0_iMMEMli];ATING HIS TWENTY-FIVE YEARS' SERVICE 



DEDICATED BY 



HIS DEVOTED PUPIL, THE AUTHOR. 



On Rapid Periodic Variations of 

 Terrestrial Magnetism. 



By 



Torahiko TERADA, Uiiiakitliakmhi. 



PART I. 

 Introduction. 



1. Immediately after the organization of the Imperial Earth- 

 quake Investigation Committee, regular magnetographic obserA'a- 

 tions were begun, on the proposal of Prof. Tanakadate, at four 

 stations, Kumamoto, Kyoto, Sendai and Nemuro, with the special 

 purpose in view of detecting any magnetic disturbances which 

 might reveal themselves associated with destructive earthquakes. 

 The instruments used were of the ordinary Mascart type. (3n the 

 other hand, a general magnetic survey of the empire was under- 

 taken, 1893-96, the result of which has been published in the 

 Journal of the College of Science, Vol. XIV. In discussing there- 

 in the local disturbing field due to Mt. Huzi, Prof. Tanakadate 

 came to the conclusion that even if the whole mass of the moun- 

 tain be suddenly removed, the disturl^ance in the vicinity would 



