PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. I. 



TABLE L. 



323 



THE PERTURBATION OF THE 15th JANUARY, 1883. 

 (PI. XXVI). 



82. The part of this day, which we now intend to study, is, as the Plate shows, that between io h 

 and 23 h 2o m Gr. M. T., the latter hour corresponding with 24 h Gottingen mean time, at which point of 

 time the observations on this term day cease. 



The first glance at the Plate shows us that during this period a number of characteristic, well- 

 defined and more or less powerful storms occur at the various stations. 



A closer examination shows that these storms would naturally be divided into several groups. 



In the first place we find in the period from io b to about I4 h a fairly well defined group of toler- 

 ably powerful perturbations. Before and after it, the conditions are more or less quiet at all the stations. 

 The curves moreover indicate that for this period the perturbation-area can be divided into two parts, 

 (i) the regions of Kingua Fjord, Fort Rae and Uglaamie, (2) Little Karmakul and Ssagastyr. 



In (i), Kingua Fjord, Fort Rae and Uglaamie, it is evident that there is a negative polar storm 

 with its centre in the neighbourhood of Fort Rae, where the deflections on the whole are greatest. 



In (2), Little Karmakul and Ssagastyr, we distinctly see the effects of a positive polar storm. 

 The forces are considerably more powerful at Ssagastyr than at Little Karmakul (note the values of e\ t 

 at the two stations), and the storm-centre of this positive storm must thus be assumed to lie nearer the 

 former station than the latter. 



It is difficult to prove with certainty the existence of any distinct movement in these systems dur- 

 ing this period, at any rate by only a direct consideration of the curves. The perturbation begins a 

 little earlier at Fort Rae that in Kingua Fjord and at Uglaamie. If we look at the close of the pertur- 

 bation, we find that the deflection in H lasts a little longer at Fort Rae than at the other two stations; 

 whereas in D the deflections last longest in Kingua Fjord. It is difficult, however, to draw any con- 

 clusion from this. 



Nor it is easy to find any distinct movement in the other system of precipitation. The deflections 

 begin more or less simultaneously at the two stations, and then increase fairly evenly. To a certain 

 extent we may speak of two maxima, the second of these being considerably greater at Little Karmakul 

 than the first, a circumstance which may possibly indicate that a removal of the storm-centre actually 

 takes place westwards towards this station. At Ssagastyr, however, the storm lasts a little longer than 

 at Little Karmakul; but no conclusion can be drawn from this fact, as the conditions at Cape Thordsen 

 are rather peculiar, and will probably exert an influence at Little Karmakul. 



If we look at the conditions at Cape Thordsen during this period, we see that the curve for the 

 horizontal intensity is very peculiar, first of all showing positive values of /-*/,, then negative values, 



