268 COMPAEISOX OF ARCTIC AND ANTARCTIC DISTURBANCES. 



about 1 Ih. 50m. The H trace shows a bay synchronous with that on the D trace, H rising as D fell and 

 conversely, but the H movements were relatively small, the rise being 17y, the fall 25y. 



It will be noticed that the large bay in the H curve occurs during the time of the first movements at 

 Kew and elsewhere, while the bay in the D curve synchronises closely with the disturbance recorded at 

 Kew near noon. 



BIRKELAND, p. 190, says that his Section (ii) extends from 14h. to 18h., but Plate XVII begins at 13h., 

 and the disturbance is said to commence at more than one place at 13h. 45m. The conclusion drawn, 

 p. 191, is that the perturbations represent "a series of short, principally polar impulses with somewhat 

 changing centre." 



The disturbances in the Arctic are not very striking, but there is a considerable movement at Sitka, 

 Kaafjord, and Matotchkin Schar with a maximum about 14h. 40m. This is also about the time when the 

 departure from the normal is largest at the non-polar stations. At Kew H fell 17y between 14h. 28m. 

 and 14h. 44m., and then returned gradually to the original value at about 15h. 50m. 



BIRKELAND'S Section (iii), 18h. to 23L, had for its principal feature in the Arctic a "violent storm . . . 

 at all the . . . stations simultaneously, most powerful at Axeloen and Matotchkin Schar," p. 192. The time of 

 commencement of this powerful storm is said to vary from 18h. 33m. at Dyrafjord to 19h. 7m. at Axeloen, 

 the time of ending being about 22h. 30m. The intensity appeared to be greatest between 19h. 15m. and 

 20h. 15m. 



At the non-polar stations the disturbance was mainly from 19h. 5m. to 20h. 30m., the maximum being 

 placed by BIRKELAND at 19h. 18m. At Kew the range between 19h. and 20h. was 48y in H and 14' -5 

 in D ; the most prominent movements were a rise of 44y in H from 19h. 18m. to 19h. 30m., and a fall of 

 14' in D from 19h. 5m. to 19h. 24m. 



In the Antarctic it does not seem possible to draw any line corresponding to BIRKELAND'S division into 

 Sections (ii) and (iii). There was a comparatively quiet time for about half an hour prior to 13h., but 

 thereafter there was a constant succession of large movements until after the time included in Plate XVII. 

 The largest of several considerable oscillations in D during BIRKELAND'S Section (ii) consisted of a fall and 

 rise each about 84' between 13h. 33m. and 14h. 28m. During BIRKELAND'S Section (iii) there were larger, 

 but not more rapid movements. Between 18h. 47m. and 20h. 40m. there was a sort of bay in the D trace, 

 a rise of 189' being followed by a fall of 151'. The decreasing movement which began about 20h. 5m. 

 was interrupted by a rise of 78' between 20h. 41m. and 21h. 13m. When resumed, it continued until 

 22h. 21m., the value of D at that hour being 261' below that at 20h. 5m. Between 22h. 37m. and 

 23h. 34m. D rose 110'. 



The H trace was off the sheet on the negative side, most of the time from 14h. 10m. until 21h. 20m. 

 Its longest appearance was from 16h. 28m. to 17h. 42m., when it rose and fell 68y, with numerous minor 

 oscillations. The chief turning-point (a maximum) was at 16h. 53m. After 21h. 20m. the H trace 

 remained on the sheet until the end of the 8th. There was rather a rapid rise of 52y between 21h. 20m. 

 and 21h. 33m., followed by a slower motion in the same direction interrupted by numerous oscillations. 

 The total range in H between 21h. 20m. and 24h. Om. was lOly. 



26. February 10-11, 1903 (hours 20-3, Plate XVIII). 



This is classed amongst the "polar elementary" storms. Of it BIRKELAND says, p. 106, "This 

 magnetic disturbance is brief, and commences without any previous equatorial perturbation on an 



otherwise very quiet day. First a small disturbance appears rather suddenly at about 21h. 6m 



most powerful at the northern stations .... but is also perceptible in (temperate) Europe and North 

 America. After about 30 minutes, the conditions are once more almost normal .... The powerful 



perturbation .... does not commence until 23h After about an hour and three-quarters the 



storm is over .... At 2h. 30m. on the llth February another short, slight perturbation appears . . . ." 

 On p. 107 BIRKELAND gives a table containing his estimate of the times of beginning and ending and 

 of the maximum for the principal storm, and also the value of Pj, the maximum disturbing force in the 

 horizontal plane. At the non-polar stations the beginning is put at about 23h. Om., the maximum 

 at about 23h. 20m. The end is given for the non-polar European stations as Ih. Om. on the llth. 

 In the Arctic the times of beginning and ending are more variable, but do not depart much from those 



