COMPARISON OF ARCTIC AND ANTARCTIC DISTURBANCES. 



273 



the 31st, rose 9''6 between Oh. 10m. and Oh. 32m., and then fell ll'-5 lietween Oh. 32m. and Ih. 15m. 

 Between Ih. 15m. and Ih. 40m. there was a rise of 2', and a further very gradual rise continued until 

 nearly 4 a.m. H fell lOy between 23h. 45m. and Oh. 6m. on the 31st, rose 25y between Oh. 15m. and 

 Oh. 42m., and fell 25y between Oh. 42m. and Ih. 27m. The only other movements on the Kew curves 

 likely to attract attention occurred shortly after 21h., I.e. 2^ hours before the commencement of the 

 "elementary polar" storm. Between 21h. 1m. and 21h. 35m. H rose 5y and fell 12y, then rose 1'Jy in 

 two steps and fell 67. The D trace shows only a very small movement about 21h. 3m., consisting of a fall 

 of 0' 8, followed by an equal rise. 



The Antarctic curves had been rather quiet for some hours prior to 19h. on the 30th, but they exhibit a 

 somewhat prominent oscillation occurring apparently simultaneously in the D, H, and V curves, all showing 

 a sharp peak at 17h. 35m. The oscillation lasts from about 17h. 31m. to 17h. 39m. In D there is a rise 

 and fall, each 12', in H a rise of 16y and fall of 12y, in V a rise and fall, each 7y. The V movement, though 

 small, is clearly shown, the curve being unusually quiet for some time before and after. The fall in D and 

 H only paused for a minute at 17h. 39m. and then proceeded for some minutes, but at a slower rate. The 

 oscillation is synchronous with the earlier movement at Kew, which occurred prior to the time considered 



by BlRKELAND. 



The next movement in the Antarctic which catches the eye occurs between 19h. 25m. and 19h. 31m., 

 with turning-point at about 19h. 28m. in all the elements. The D movement is small and not very 

 distinct. It consists apparently of a fall of about 2' and a rise of 10'. H falls and rises 18y, while V falls 

 and rises 67. These movements synchronise with the second of the two movements at Kew, i.e. with 

 BIRKELAND'S " equatorial " perturbation. One is rather reminded of the occurrence of the two oscillatory 

 movements on March 22 ; the interval between the two movements is nearly the same on the two 

 occasions. The movements of March 30 do not appeal so much to the eye as those of March 22. 



The fact that the disturbances in the Antarctic are again larger than the corresponding ones at stations 

 nearer the Equator will doubtless have been noted. 



Though not seriously disturbed, the Antarctic curves all show oscillations of increased amplitude 

 between 19h. 25m. and 21h. 40m. The largest movements during this time consisted of a bay, apparently 

 simultaneous in the three traces, from about 21h. 6m. to 21h. 26m. During it D fell 35' and rose 52', 

 H rose and fell 26y, while V fell 25y and rose 38y. This movement, it should be noticed, occurred at a 

 time when the curves at Kew and the other non-polar stations showed increased activity of disturbance. 



From 21h. 40m. to 22h. 25m. there was a relatively quiet time in the Antarctic. There then ensued 

 from 22h. 25m. to 23h. 30m. an interval during which the V trace showed a number of rather sharp 

 oscillations, which were accompanied by more or less simultaneous oscillations in D and H, the H oscillations 

 being of enhanced size. Several of these oscillations rather suggest the " special type " of disturbance, 

 but their period is short and the rises in V do not exceed the falls. The two following cases gave the 

 largest changes in V : 



The oscillations in V continued for some hours, but with diminished size. In the case of D and H, 

 however, movements of increased size and duration took place. 



The chief movements in D were a fall of 99' between 23h. 30m. on the 30th and Oh. 20m. on the 31st, 

 a rise of 120' between Oh. 20m. and Oh. 56m., and a fall of 111' between Oh. 56m. and Ih. 57m. These 

 movements were accompanied by shorter oscillations of comparatively small size. 



During this time there was a large bay on the H curve, but its nature is imperfectly shown, as the trace 

 was off the sheet on the positive side from Oh. 16m. until Ih. 7m. Between 23h. 40m., when the bay may 



2 N 



