PART I. ON MAGNETIC STORMS. CHAP. III. 



Current-Arrows for the 1st November, 1902; Chart XIX at 



251 



l h O m . 



Fig. 1 1 6. 



THE PERTURBATIONS OF THE llth & 12th OCTOBER, 1902. 



(PI. II). 



68. From ii h on the nth October, to about o h 30 on the I2th, perturbations that are some- 

 times violent are noted at all the stations from which we have observations. They are unusually violent 

 in the equatorial regions, where the conditions become rather complicated, as there are undoubtedly often 

 several current-systems, sometimes even occurring simultaneously. 



The perturbations seem to fall naturally into three principal sections, 

 The first from n h to I7 h .2o m on the nth October, 

 The second from iy h 2o m to i8 h 3o m on the nth October, and 

 The third from i8 h 30"" on the nth October, to o h 30 on the izth. 



In the first section, it is especially in the horizontal intensity that the perturbation occurs. We see 

 that the perturbing force allmost everywhere is directed northwards along the magnetic meridian. The 

 way in which the force is generally distributed during this period is shown on Chart II, for I7 h o m . 



It appears from the copies of the curves, that this part of the perturbation is especially well deve- 

 loped in the equatorial regions. This, together with the serrated character of the horizontal intensity 

 curve, and the direction of the force, would make it appear that this is mainly a positive equatorial 

 perturbation of the well-known type (cf. e. g. Art. 27). 



