PART I. ON MAGNETIC STORMS. CHAP. III. 231 



At Sitka too, this storm occurs with a violence that approaches what we find at the Norwegian sta- 

 tions, this being greatest between i3 h i5 m and I4 h , at which time the H variometer-needle is deflected 

 out of the field. This storm occurs at the same time as the first great intermediate storm at Axeleen. 

 Great storms also occur at the other stations in the western hemisphere; and even at Honolulu the 

 perturbation on that day is fairly powerful. In the United States the character of the perturbations 

 varies more or less with time and place. Unfortunately we here only have registerings for the first 

 part of the perturbation. 



In Central and Southern Europe the perturbation is rather considerable though relative to that in 

 the equatorial stations comparatively slight, especially the first part. Up to ij h 45"" the conditions remain 

 fairly uniform a deflection in H, indicating a decrease in the horizontal intensity, and a westward 

 deflection in D. At about ij h 45, the .D-curve goes over to the opposite side of the mean line, while 

 the deflection in H is increased. The D-curve of San Fernando forms an exception to this; as the 

 change in direction here does not take place till about 2 hours later. The course somewhat resembles 

 that at Kaafjord, as the change in D takes place at about the same time as the above-mentioned change 

 in the amplitude. Between 23 h and o h 35 there is a rather strong impulse in D, this being simultaneous 

 with the second powerful storm at Axelaen. 



In the region of Dehra Dun, Batavia and Christchurch, the storm is very powerful, the first part 

 of it being even more powerful than in England, France and Germany. At I2 h 30, the perturbing 

 force at Dehra Dun attains a value of 80 y. 



The conditions on the whole are fairly simple. At Dehra Dun for instance until 13'' I5 m the 

 perturbation is noticed principally in H and then there also is a deflection in the declination towards the 

 east. Similar conditions we also find at the other stations. The deflection in H is uniform in direction 

 throughout, as H is decreasing all the time. The character of the curve is quiet on the whole, without 

 any great, sudden changes; and only at about I3 h 30 is there such a change in the deflection. 



It appears from the coincidence of the previously-mentioned powerful storm at Sitka with that on 

 Axeloen, that these deflections are connected with one another. The perturbation on this date resembles 

 in many respects the preceding perturbations of the I5th and 8th February and that of the 27th Octo- 

 ber. We may thus make a comparison with the perturbation of the 27th October for instance. On this 

 day we also found a storm of long duration, that was especially powerful and of similar effect in the 

 south Asiatic districts. During that perturbation there was an intermediate storm that was also powerful 

 in the districts of Dehra Dun and Batavia, and was almost the reverse of the long storm. 



A little before midnight there was another short storm, the effect of which was very slight at 

 Dehra Dun, but powerful in Europe. The chief difference is that the long storm of the 3ist October 

 is much more powerful and of much longer duration, so that both the short storms come within its 

 limits. The first intermediate storm, moreover, occurs a little earlier in the day, and the second a little 

 later, than those on the 271)1 October. 



Analogous with what we have done in the case of the last described storms this perturbation is 

 divided into three principal phenomena, the long storm and two intermediate storms. There are indeed 

 more interruptions than these two during the long storm, that might well be studied, for there are in- 

 numerable small interruptions; but as far as we can tell from our material, it is only these two that 

 have a universal and powerful effect, and between them and the other irregularities there is a wide 

 gulf that cannot be crossed without leading to so great a multiplicity, that the main lines would be lost, 

 and the study of the phenomena rendered nearly impossible. 



