THE DAILY FIELD OF MAONETIC DISTURBANCE 



BY 



Dr. W. van BEMMELEN. 



It has long since been known, that magnetic force on 

 days ot' disturbance shows a eharacteristic deviation, both in 

 amount, and direction, from the norinal vakie on quiet days. 

 In 1895 ') the author inquired into this phenomenon af ter 

 a method shortly described below. 



Oalling- h^, d^, v^; h^, d^, v^; h,, d,, v,; h3, d., V3, etc. 

 the daily means of liorizontal intensity, declination and vertical 

 intensity resp. on a day of disturbance and subsequent quiet 

 days, for a number of n cases the mean values 



„ hl. 8 -|- h2.s -\ hn.s dl.s -{- dz.a -\ dn.8 



-H= y D^ = 



v„ = 



n 



Vl.8 + V2.S -| Vu.3 



n 



„ hii + ha.i -| hu.1 di.i -\- A2.1 -\ dn.i 



1 n ^ n 



Vl.l -|- V2.I -| Vn.1 



V, = 



n 



H^ = etc. 



were computed. 



The vaUies (H^— H„^) and H(D^— D,,,), H being the mean 

 value of the horizontal intensity, determine the horizontal 

 component of the average dift'erential vector for the day 

 of disturbance and the m*th following day. The angle ^ 



1) Meteorol. Zeitscht'. 1895, p. 321. 



