128 A. TANAKADATE. 



All these three surveys give the line of no current through 

 the middle of the country ; in Japan the current is upward on 

 the Pacific side and downward on the Siberian side ; in Austria 

 it is upward on the north and downward on the south ; in Great 

 Britain, upward on the east and downward on the west. 



Whether these distributions of current density show the real 

 average state of things during the surveys of the respective coun- 

 tries or not is very doubtful. The fact that the line of no current 

 runs thi'ough the middle in each of those countries inspite 

 of different aspects of their distributions, seem to indicate that 

 they are the result of uncompensated local disturbances and 

 inadequacy of the empirical formuhe to a large extent, if not 

 wholly. Considering that these currents depend upon the dif- 

 ferences of differential coefficients of the ol)served elements, ob- 

 servations of greater refinements than the present, both in con- 

 struction of instruments and distribution of stations, will be 

 necessary in order to settle the question more definitely ; certainlv 

 these currents can be accounted for by the probable errors in 

 the constants of the empirical formulse, at least in the case of 

 Japan. Even in Great Britain, where the survey was very care- 

 fully carried out by excellent hands, the two sets of lines of 

 equal currents present very different appearances according as they 

 are derived from the district equations or general equations for 

 the whole country (See Map 9a). 



Under such circumstances the most fascinating subject of 

 the motion of electricity from or towards the earth's surface 

 must be left untouched, be it due to the diurnal motion of the 

 earth or transference of ions with water vapour and the like. 

 These will probably be better elucidated by pursuing other 

 methods of investigation. It may l)e a good plan to improve 



