PART I. ON MAGNETIC STORMS. CHAP. III. 187 



THE PERTURBATIONS OF THE 7th & 8th FEBRUARY, 1903. 



(PI. XVI & XVII). 



59. The storms now to be described, some of them powerful ones, break in upon a very long period 

 of calm, which may be said to have lasted with single exceptions since the cessation of the storms at 

 the end of November, 1902. 



This interruption of the quiet conditions occurs suddenly at the Norwegian stations with a fairly 

 powerful storm, commencing at 2i h 5, on the 7th February, and lasting, at Kaafjord, until about i a. m. 

 on the 8th Februay. 



The first perturbation on the 7th does not belong to the series of perturbations mentioned in the 

 circular, and our material is therefore not sufficiently complete to allow of our investigating it more fully 

 in southern latitudes. As it happens, however, registerings for this date have also been received from 

 a few stations in addition to the Norwegian stations, namely from Kew, Wilhelmshaven, Munich, Toronto 

 and Christchurch. Judging from the conditions at these places, we here have a typical polar elementary 

 storm, with its centre near the Norwegian stations. 



This storm is not succeeded by calm, however. Towards morning on the following day, there are 

 varying precipitations about the auroral zone. Between 2 h and 5'' for instance, there are powerful 

 storms round Axeleen; and they are also very powerful in Toronto. In southern latitudes too, there is 

 constant disturbance as time passes. 



From 9 h to n h on the 8th there is a perturbation that is especially powerful at Sitka and the 

 American station, and is accompanied by simultaneous perturbations all over the northern hemisphere and 

 over the southern right down to Christchurch. 



Commencing with this perturbation, we will study the conditions more carefully, although in the 

 first place it is the powerful polar storm, with a maximum at about ig h 25 on the same day, to which 

 we have especially turned our attention, and which is given in the circular. 



As we must confine ourselves to a study of the chief features of the perturbations, we shall here 

 mainly give our attention to three periods of time, in which the perturbations are particulary powerful. 

 It will easily be seen from the conditions at Sitka that a division such as this is the natural one, the 

 three sections being: 



(1) the above-mentioned perturbation from g h to n' 1 , 



(2) a perturbation between 14^ and i8 h , and 



(3) the period from i8 b to 23 h . 



The curves for the second and third periods are shown on the same plate, those for the first 

 being separate. 



THE PERTURBING FORCES. 



60. The first section (PI. XVI). 



The perturbation is particularly powerful at Sitka, and is especially violent from g h to g h 35 m . 

 Simultaneously at the other stations in the New World, there are fairly powerful perturbations; and we 

 see directly from the curves that the conditions vary greatly from place to place. We shall find, for 

 instance, a considerable difference if we compare the //-curves for the three stations, Toronto, Chelten- 

 ham and Baldwin. At Toronto there is a long, rather powerful perturbation, as also at Cheltenham, 

 both showing a diminution in H. At Baldwin, on the other hand, H remains almost normal, if anything 

 a little too great during the perturbation. At Honolulu there is a faint but distinct perturbation in 

 declination, coinciding with the perturbation farther north. In H too, there is some resemblance in the 

 form of the curve to that of the declination-curves for the three eastern stations in North America, as 

 a comparison with the declination-curve for Cheltenham will at once show. A peculiarity is now apparent, 



