256 COMPARISON OF ARCTIC AND ANTARCTIC DISTURBANCES. 



21y, and fall, 14y, actually shown were probably a good deal exceeded. After Oh. 53m. the oscillatory 

 movements in the V curve were much reduced. The D trace, however, showed two moderate bay*. 

 During the first from Oh. 53m. to Ih. 16m. D rose 33' and fell 69'. During the second from Ih. 16m. 

 to 3h. 23m. D rose 42' and fell 70'. Between Ih. 39m. and 2h. 17m. H fell and rose 39y. The trace 

 went off the sheet at 2h. 17m. and did not reappear until 3h. 27m. It went off and came on steeply, so 

 there may have been a considerable movement in the interval. 



13. October 27-28, 1902 (hours 14-1, Plate IV). 



This "compound" disturbance is divided by BIRKELAND, p. 209, into two sections. The first section, 

 from 14h. to 20h. 30m., is regarded as composed of a long storm, largest on the whole in the Equator, 

 during which there is an " intermediate " storm, most powerful in the Arctic, especially at Axelden and 

 Matotchkin Schar, which lasted from about 15h. 30m. to 16h. 45m. 



At Kew, which was fairly representative of non-Arctic Europe, the most prominent phenomenon of 

 Section (i) we a bay in the D curve from about 15h. 30m. to IGh. 55m., the element being depressed. 

 The greatest departure from the normal value was about 7' and occurred about 16h. 20m. The corre- 

 sponding H movement was a fall of 22y from 15h. 15m. to 16h. 5m., interrupted by two small recoveries, 

 and a rise of 19y from 16h. 5m. to 16h. 30m., followed by a smaller fall. 



BIRKELAND'S Section (ii), from 21h. 40m. to about midnight, consisted of a "polar" storm, largest at 

 Axeloen. A table on p. 212 gives particulars of its beginning and end and also as to the time of 

 occurrence and the value PI of the largest disturbance in the horizontal plane. The commencement is 

 about 21h. 40m. and the hour of maximum about 22h. 50m. at most stations; the end varies from 

 23h. 20m. on the 27th to Oh. 20m. on the 28th. PI varies from 265y at Axeloen to 4y at Dehra Dun, the 

 value at Kew, 29y, being slightly above the average for non-Arctic European stations. 



The general nature of the disturbance during Section (ii) outside the Arctic is fairly represented by the 

 phenomena observed at Kew. D there was distinctly depressed from 21h. 40m. on the 27th until about 

 Oh. 10m. on the 28th. The most rapid change was a fall of 3' between 22h. 20m. and 22h. 45m. II, 

 on the other hand, was distinctly above the normal value from 21h. 40m. to 23h. 20m. The maximum 

 occurred about 22h. 54m., and the most rapid change was a fall of 20y between that hour and 23h. 34m. 



The Antarctic curves during the time covered by Plate IV show a moderate amount of disturbance, but 

 nothing, perhaps, that would naturally attract attention. During the "intermediate" storm of BIRKELAND'S 

 Section (i) there was a bay on the D curve between 15h. 29m. and 16h. 53m., the element rising 47' and 

 falling 33'. The V trace showed numerous oscillations, but the largest only 3y or 4y in amplitude. The 

 H trace was beyond the limit of registration in the negative direction from 15h. 43m. to 16h. 53m., and 

 may of course have been considerably disturbed. 



The largest movements recorded during Section (i) took place later, between 18h. 53m. and 19h. 53m. 

 During this hour D rose and fell 66', H rose 99y, while V fell 1 4y and rose 35y. 



The D trace was off the sheet on the positive side for some time after 21h. and there was no trace from 

 22h. 16m. to 22h. 36m. There is thus rather a lack of information as to what was happening during 

 BIRKELAND'S Section (ii). After 22h. 36m., when registration was resumed, there was no really striking 

 D movement. There was, however, a small bay between 23h. 16m. and 23h. 56m., the value rising 18' and 

 falling 30'. The H trace, which had just got off the sheet on the positive side at 22h. 46m., came on again 

 at 22h. 47m., and between that hour and 23h. 33m. H fell 53y. After 23h. 33m. H rose gradually with 

 minor oscillations until Oh. 53m. on the 28th, when the trace again went off the sheet on the positive side 

 and remained off for two hours. 



V fell 32y between 22h. 36m. and 23h. 17m., and rose 40y between 23h. 17m. and 23h. 43m. After a 

 slight halt it continued to rise, but much more slowly, until Oh. 17m. on the 28th. Between Oh. 17m. and 

 Oh. 45m. it fell 19y. Thereafter the V trace was relatively quiet for some hours. 



14. October 28-29, 1902 (hours 14-1, Plate V). 



This was another " compound " storm, which resembled that of the previous day in containing two " inter- 

 mediate " elementary polar storms. The interval between these was, however, much less than on the previous 

 day, and there was, according to BIRKELAND, p. 222, in lower latitudes, " 110 trace on the 28th of the long 

 storm that occurred on the 27th, and was especially powerful at the Equator." According to BIRKELAND'S 



