200 KNOTT AND TANAKADATE 



WO were compelled liy very wet weather to innke onr (observations on 

 the stone pillars in the meteorological observatory,* and this may have 

 been a source of disturbance. 



If we now express the c<vordirintes in kilometres, the Formula 

 for the Di]) becomes 



d = 50° 28' .6 -f ( .6168 9 — .1044 X )' 



Let u be the angle between the Line of Equal Dip drawn eastward 

 and the longitude line drawn northward ; and let r be the rate of 

 change of Dip per kilometre of distance measured in a direction per- 

 pendicular to the Line of Equal Dip ; then we find in the usual way 

 for the menu station 



n = S0° 23' .6 

 r = 0' .626 



IL — The Horizontal Force. 



The fifty selected observations, when combined by the method 

 (<f least s(|uares, gave the following formula expressing the Horizon- 

 tal Fo7-ce ( H) in terms of the co-ordinates : — 



H = .29482 — .0000617 9 — .0000117 X 



7Î is measured in absolute 0. G. S. electro-magnetic units ; and 

 ? and ^,the latitude and longitude co-ordinates referred to the mean 

 station (06° 30' N". Lat., 137° 9' E. Long.), are measured in minutes 

 of arc. 



In the annexed table. Table III., the values of the Horizontal 

 F^w(V as (ol^served at all the stations are given, and alongside of them 

 the values as calculated from the Formula. As before the selected 

 stations are indicated by having their numbers printed in heavier type. 



* The observatory is Imilt wholly of wood; l.nt tho tile-roof or the stone pillars them - 

 gejves may have l)Pen a.pprecia))ly mao-netic. 



