20ß 



KNOTT AND TANAKADATE 



very ohvioii S Icind of disturbance. Take, for example, the first pair. 

 Köfii, the more northerly station, has an increased dip and a diminished 

 horizontal force ; Avhereas Hakone. the more soutlierly station has a 

 diminished dip and an increased horizontal force. Now this is 

 exactly whnt Avonld happen if between the two stations there existed 

 material t^f magnetic ]ierrneability greater than the average for the 

 earth's crust. But avc know that these stations are separated by 

 rocks, which presumably belong to the Aolcanic system of Fnji-yama, 

 and are almost certainly highly magnetic. It is not at all surprising 

 to find such huge disturbances ; but it is peculiarly interesting to find 

 that the disturbance in the Dip largely accounts for the disturbance 

 in the horizontal force, the total force being comparatively slightly 

 affected. This Köfu-Hakonc disturbance falls in remarkably well 

 with our preconceived ideas as to the perturbing effect of volcanoes 

 upon magnetic distribution. 



The other pair of stations, Hagi and Hamada, present exactly 

 the same magnetic features. Thus it is Hamada, the more northerly 

 station, which has the increased dip and the diminished horizontal 

 force. It corresponds therefore to Köfu. Magnetically considered, 

 Hamada and Hagi are just a repetition of Köfu and Hakone. But 

 here the likeness apparently ends ; for between Hamada and Hagi no 

 important mass of volcanic rocks is known to exist. Of course 

 there are magnetic rocks other than volcanic ; and the apparent 

 absence of the latter does not necessarily imply the absence of the 

 former. All we can say is that between Hagi and Hamada a more 

 than usually magnetic mass lies. 



A careful scrutiny of the various tables of differences does not 

 reveal any distinct tendency for the stations to occur in gri^ups, 

 excepting in one case only. That exceptional group embraces the 

 Kyushu stations. For them both the dips and total forces are smaller 



