MAGNETIC SURVEY OF JAPAN FOR THE EPOCH 1895.0. 175 



§ 14. DISTURBING FORCES. 



The differences of the observed and calculated values of rect- 

 angular components given in Table XV, under the headings 

 JX, JY, IL are taken to be those of the disturbing force at a place, 

 follo\Ying the plan of Profs. Rücker and Thorpe. The result- 



tant force =^^JX"+T/Y'^+ JZ", its asimuth and altitude are given 

 in following columns of tlie same table. By way of control tliese 

 elements were calculated from the differences of observed and 

 calculated values of declination, dip and horizontal intensity in 

 Table XIV by the formula 



JX = cos o JH— Hsin o Jo 

 JY-sin<5 JH+Hcoso Jo" 

 JZ=tg<9 JH+ sec^^Ho"^ 



giving results which agreed very closely with the former, except 

 in cases of extravagant differences such as those obtained in Huzi 

 and Asama. 



In Map 10 the horizontal components of the disturbing forces 



-v/JX' + JY^ are represented in magnitude and direction by black 

 lines with arrow heads starting from each station. In a few places 

 where the determination of the declination fails, the magnitude 

 of the difference of the observed und calculated values of the 

 horizontal intensity JH(=JX), is indicated by vertical lines without 

 arrow heads extending both ways through the point. The vertical 

 component JZ is represented by a blue or red line according as 

 its direction is downward or upward. The scale of intensity is 

 1 mm. for 100 ï or 0.001 C.G.S. unit of magnetic force for either 

 component. 



