218 



KNOTT AND TANAKADATE 



We shall now bring together for ease of reference the values of 

 the elements for the mean station, the directions in which the iso- 

 magnetic lines pass through this station, and the maximum rate of 

 change of each element per kil(jmetre of distance. The tabulation of 

 the declination constants offers some difficulty, as the isogonic lines 

 are not straight l)ut paraboUc. If, however, we express the latitude 

 and longitude co-ordinates in kilometres, we obtain the following 

 transformed expression for the declination : — 



= 4° 53'.3 + [.1303 9 - .0732 X - .000104 X']' 

 From this we may estimate the constants u and r, not only for the 

 mean station, l)ut also for other stations. It is easy to see that the 

 values of u and r will be the same for all points having one and the 

 same longitude. In this way the following table has been constructed ; 

 u being, as formerly defined, the angle made by the direction of the 

 iso-mao"netic line drawn eastward and the meridian line drawn north- 

 ward, and r representing the rate of change per kilometre in a direction 

 perpendicular to this line. 



And, finally, collecting the results for the mean station ( 36° 30' 

 N. lat. and 187° 9' E. long.), we have the following condensed table 

 of the magnetic constants of the mean station as calculated from Fifty 

 selected stations conveniently distributed over all Japan. 



