176 A. TAXAKADATE AXD H. NACIAOKA. 



If we take Mr. Sekino'ö results in tlie iiciglibourliood of iNagoy.'i 

 as consiöteut among" themselves, the course of the hlnes of equal 

 horizontal iriieusity is very differeut from either of the two systems 

 we obtained, as shown by dots in Tl. A IX. Considering that tlie course 

 of these curves will be independent of the instrumental constants, 

 we feel sure of the fact that these lines have Ijeen underg<3ing 

 considerable variation during recent years about the Nagoya district. 



The fact that the horizontal intensity has suftered the most 

 disturbance, seems to show that the seat of that disturbance, if it 

 exist at ah, does not lie at great depth; and this is further confirmed 

 l)y the smallness of the disturl^ances of all the other elemeüts. 

 Examining the chart that was provisiorially prepared for the rep(jrt 

 of the previous surve}^, Avhich is more detailed than the one published, 

 Ave find the same kind of disturbance near Ilamada — namely 

 conAcrgence of the lines of equal horizontal intensity towards the 

 place; and we n(_)w recollect that it was here that the eartlupiake, 

 wliich was tlie severest one preceding the present, Avas felt in 

 1872. AVhether this disturljance is due to the change of magnetic 

 condition of the earth's crust in the vicinity caused by strain, or to the 

 change in conductivity for earth ciu-rents, or, again, is the result of the 

 dislocation of the magnetic crust, is more than Ave can decide from 

 the scanty data Avhich AA^e now possess. These points Avill undoubted- 

 Iv afford most interesting- subjects of research in the future. 



