PART I. ON MAGNETIC STORMS. CHAP. III. 377 



At Christchurch there are also powerful storms at this time, both in H and in D, lasting far 

 longer than the period we are now considering. 



Finally, in America there are also powerful storms, during which the deflections in H are negative 

 all the time, whereas in D, while sometimes very powerful, they are more variable as regards the 

 direction of the perturbing force. 



On Charts III VIII are shown the various fields that appear during the various phases of the 

 perturbations in this section. 



We have already remarked that the perturbation-conditions as a whole are to be understood as a 

 long, more or less constant, perturbation, going on all the time, accompanied by several intermediate, 

 short, but powerful storms. The latter will now form fields, which, as a rule will differ to some extent 

 from those produced by the long storm. The form of the field answering to the long storm will thus 

 be more or less obliterated during these intermediate storms. In the earlier perturbations, similar long 

 storms, interrupted by short, intermediate storms, have continnally been found, and their conditions have, 

 as a rule, been comparatively so simple, that it has been possible to separate the two phenomena. 

 Here, however, the conditions during the long storm are so disturbed, that it has not been possible to 

 take out the intermediate perturbing forces, although conclusions as to their behaviour may be drawn 

 from the form of the curves. 



The conditions which we have been led to consider as the typical ones, are, as we have 

 already said, a combination of negative and positive polar storms, the former occurring prin- 

 cipally on the night-side, while the latter are characteristic of the day-side, and in latitudes that as a 

 rule are a little more south than those in which the negative storms attain their greatest strength (see 

 Art. 69). The position of these systems may of course vary somewhat, according as the conditions 

 under which the perturbations are formed alter. In addition to these polar precipitations, there have 

 also been, as we have often seen before, simultaneously-acting storms of types that should be due to 

 stiffer rays, which acted most powerfully in low latitudes. Rays of this kind do not appear to have had 

 any specially noticeable influence during this perturbation. We shall find, however, that the conditions 

 as a whole may be referred to two polar systems of the two types mentioned above; and we shall thus 

 receive fresh confirmation of the correctness of our former assumptions. 



The resemblance between the fields is quite striking, even on a casual glance at the various charts. 

 The typical form of the field is most clearly seen in the charts in which Ekaterinburg and Irkutsk are 

 also shown. These charts are only marked for the full hours 23 b , 24'' and 2 1 ', as has generally 

 been done when the conditions varied considerably from time to time. They distinctly show an area 

 of convergence of most characteristic form in the district Europe and Asia, but displaced a little on the 

 various charts in a direction east and west. We find the same conditions at the other hours in the 

 case of most of the stations. At the stations of Southern Asia, on the other hand, the conditions are 

 often rather peculiar, and the perturbing forces sometimes directed the opposite way to that one would 

 expect to find as the effect of the long polar night-system. The current-arrows, however, are as a 

 rule very small, and therefore the accuracy with which the directions are determined is considerably 

 less. Uncertainty in the position of the normal line will exert a considerable influence. Sometimes, 

 however, the deflections are so great that it cannot be put down to inaccuracy alone; and we are then 

 obliged to assume that there are other forces asserting themselves. This, for instance, is the case on Chart 

 VI for o h 50 on the 24th. In order to explain these, it might be well to see whether here, too, there 

 were not an equatorial storm such as we have often found before. Although it is not impossible that 

 a storm such as this may be acting here, there is nothing that decidedly points in that direction. On 

 the contrary it seems more probable that these deflections are produced by a more or less intermediate 

 positive polar storm, such that would act in these districts. In the first place, the stations in the 



