PART I. ON MAGNETIC STORMS. CHAP. III. 27! 



atic stations is fairly quiet, with the exception of the districts surrounding the intermediate storms, a 

 peculiarity which we found to be characteristic of this kind of equatorial storm. In the second place, 

 the conditions in P, also give a similar indication. A negative equatorial storm in the northern hemi- 

 sphere will produce vertical arrows directed downwards, while the system that should form the area of 

 convergence would produce vertical arrows directed upwards. 



At first, it is true, positive values of P, are found at Pawlowsk, Ekaterinburg and Tiflis, when 

 the polar storm is still comparatively slight (see Chart V); but when the latter has developed consider- 

 able power, we must imagine that the greatest effect of the polar system is in the north. We now 

 find all the time, moreover, negative values at Pawlowsk and Ekaterinburg (see Charts VI and XI 

 XIV); while on Chart VI P, is still positive at Tiflis. This subsequently diminishes at Tiflis too, be- 

 coming for the most part zero (Charts XII XIV), and sometimes turning a little round to the opposite 

 side (Chart XI). At those stations of Western Europe from which we have observations of the vertical 

 intensity, we find throughout positive values of P v , though sometimes zero. We may imagine this 

 circumstance to be partly caused by the positive polar system of precipitation, which produces positive 

 values of P e in the area of divergence, but also partly by the assumed negative equatorial storm, which 

 will here operate in the same direction. One might perhaps be tempted to believe that this last polar 

 system might possibly produce the positive values of P, at the more eastern stations; but this is not 

 possible if the systems are at all of the constitution we have supposed. If, for instance, on Chart V, 

 the vertical arrow at Tiflis were solely due to this positive polar system, the horizontal arrow produced 

 by this ought at least to be as large as the one really found there. It seems impossible to explain this 

 circumstance by comparison with the size of the current-arrows in Europe and America ; and as regards 

 Chart VI it is still more difficult to imagine that this system, which, in all probability, should be considered 

 as comparatively weaker than the more easterly one, should have a greater effect at Tiflis than the last- 

 named storm, which is moreover nearer to that station. 



There thus seems to be sufficient reason for supposing that this is really a storm that acts most 

 powerfully at the equator, and is of the nature of the so-called negative equatorial storms. 



We hereby also get a comparatively simple explanation of these fields as only the result of a simple 

 cooperation between the already-described elementary phenomena. 



We will in conclusion refer to the remarks that have been made concerning the positive value of 

 P, at Tiflis, which, in several of the storms described, has occurred in similar areas of convergence, 

 e. g. in the perturbation of the 26th December, 1902 (Charts I and II, and especially the description 

 on pp. 137 and 138), and that of the 15th February, 1903 (Charles V and VI, with description on 

 p. 178). In these earlier cases, we could not come to any definite decision regarding the systems which 

 produced this apparent abnormal value ; and we only suggested the possibility that these storms resembled 

 the cyclo-median perturbations. Here, however, it seems more probable that the type resembles the 

 negative equatorial storms. 



The fourth polar storm, or first intermediate storm, is shown on Chart IV. The field here does 

 not differ essentially from that described under the third polar storm. We can only imagine the altera- 

 tion to be produced by the fact that the positive polar system, which we supposed existed there, now 

 undergoes a sudden increase in power and extent, so that it reaches beyond Matotchkin Schar. The 

 arrow at Irkutsk, moreover, in connection with those at Honolulu and Sitka, indicates, though faintly, 

 an area of convergence in that district; and the arrow at Axeleen ought probably to be interpreted as 

 a continuation of this more easterly system. We must here, however, be careful not to draw too 

 certain conclusions from the conditions at Irkutsk, for we have only hourly observations to go upon. 



The fact that these two systems of precipitation work into one another, is one that we have often 

 observed before, especially in the case of Matotchkin Schar, e.g. in the intermediate storms of the 



