THE DISTURBÂ^'CE OF ISOMAGNETICS. 155 



Soil : — Loam, 



Shicya ^ = 36° 18', / = 136° 14' 



South shore of the Japan »Sea, 150 metre.s N of the crema- 

 tion buildina'. 



Soil : — Mostly quartz and felspar fragments. 



Isshiki if = 34° 30:4, ; =. l3o' 45:3 



Middle of salt farjn, former site of fort. 

 Soil : — Derived from slaty rocks. 



Instruments and Method of Observation. 



The object of the present survey being to get results closely com- 

 parable with those obtained in the previous one, we took the set of 

 instruments that was used by the ' south ' party of 1887, for the sake 

 of eliminating instrumental peculiarities should there be arjy ; since 

 the regions to be visited had then been exclusively surveyed by that 

 party. Of the instrumental constants we give new determinations 

 somewhat in detail. 



Declination Coil. — Its length is 13.3 cm.; breadth, 13.2 cm.; 

 height, 2.7 cm.; the space unwound in the middle 2.4 cm.: thus 

 nearly fulfilling the condition for minimizing the error due to ex- 

 centric position of the magnetometer, in which the ratios of these 

 dimensions arc 5; 5 : 1 : 1. The coil is wound in two layers, the 

 under layer with somewhat fine wire to 22.2 turns per cm., and 

 the upper one with thicker wire to 13.2 turns per cm., making- 

 in all 35.4 turns. The field at the centre is 6.5 x 35.4-:- 10 -=23 per 

 ampère, or 0.013 ampère will give .3, the approximate value of H in 



