COMPARISON OF ARCTIC AND ANTARCTIC DISTURBANCES. 201 



17. November 23-24, 1902 (hours 15-7, Plate VIII). 



This "compound" storm, divided by BIHKELAND into three sections, is said, p. 272, to bo the most 

 powerful of a series which developed daily in the Arctic from the 19th to the 26th of November. 



Section (i), from 15h. 20m. to about 16h. Om., is described, p. 273, as a "typical positive equatorial 

 storm," " strongest at the equatorial stations in the South of Asia." BiitKKi,AND speaks of a sudden rise 

 occurring in H at 15h. 30m., except at the American stations, where the rise is slow. The time is not, I 

 think, intended to be exact. For at Kew H begins to rise at about 15h. 22m., rising lOy to a rounded 

 maximum at about 15h. 32m., and then diminishing about 6y during the next 7 minutes. There was a 

 corresponding small movement in D, whose maximum was, however, a few minutes later. These trifling 

 movements which can, however, be recognised at Axelden, Kaafjord, and all the European and Southern 

 stations -constitute the largest disturbance of Section (i). 



During Section (ii), from IGh. to about 22h., the disturbing forces are generally small, but from 

 17h. 30m. to 18h. 20m. the disturbance is somewhat greater, " especially in southern latitudes." 



In the Arctic BIRKELAND sees indications of a " polar " storm of minor intensity. During this time the 

 most noteworthy feature at the non-polar European stations is a bay on the D curve, extending from 

 about 17h. Om. to 18h. 30m. at Kew, where the element fell and rose about 3'. The most prominent H 

 changes at Kew were a fall of 12y between I7h. 23m. and 17h. 35m., and a fall of lly between 19h. 52m. 

 and 20h. 3m. 



BIRKELAND'S discussion of his Section (iii), 22h. to 7h., appears involved. He attempted apparently to 

 recognise a series of " elementary polar " storms in it, but was unable to disentangle them. Speaking 

 generally, the Arctic curves show numerous rapid oscillatory movements going on pretty continuously all 

 the time. 



At the non-polar stations the most disturbed time was from 22h. on the 23rd to 3h. on the 24th. The 

 movements during this time were really of some size. At Kew, for instance, D fell 10' between 22h. 5m. 

 and 22h. 42m., rose 5' between Oh. 30m. and Oh. 50m., fell 6' -8 between Oh. 50m. and Ih. 20m., rose 10' -4 

 between Ih. 20m. and 2h. 10m., fell 9' between 2h. 10m. and 2h. 43m., and rose 7' between 2h. 43m. and 

 3h. 12m. H fell 37y in three steps between 21h. 48m. and 23h. 1m., rose 35y in two steps between 

 23h. 1m. and 23h. 42m., fell 29y in two steps between 23h. 42m. on the 23rd and Ih. 35m. on the 24th, 

 rose 42y between 2h. 2m. and 2h. 24m., and fell 30y between 2h. 48m. and 3h. 52m. 



The conditions existing at the southern stations during the early morning of the 24th will be best 

 realised by consulting the Christchurch H curve given in Plate XV of the present volume. 



In the Antarctic there were some very rapid oscillatory movements synchronous with the commencing 

 movements seen at Kew and elsewhere which BIRKELAND characterised as " equatorial." The D move- 

 ments were so rapid that the turning-points are not very clearly shown, and the following measurements 

 may be slightly under-estimates. Commencing suddenly, during a fairly quiet time, we have between 

 15h. 21m. and 15h. 37m. a rise of 81', a fall of 78', a second rise of 60' and a second fall of 85', with minor 

 oscillations during the larger movements. There were presumably corresponding movements in H, as the 

 curve which had been off the sheet for some time on the negative side came on for a couple of minutes 

 about 15h. 24m., forming a very sharp peak (maximum). During the second oscillatory movement in D 

 there was a marked depression and recovery in V, of amplitude 44y. After this commencement the 

 Antarctic curves remained highly disturbed until lOh. on the 24th. They are reproduced from Oh. 18m. 

 to lOh. 31m. (or 11.25 a.m. to 9.38 p.m., L.T.) in Plate XXV of the present volume. The most 

 conspicuous movements prior to the time covered by this plate were as follows : 



D after falling 226', with numerous oscillations, between 15h. 28m. and 16h. 25m., rose again, oscillating 

 vigorously, about 197' between 16h. 25m. and 18h. 8m., and then fell 127' between 18h. 8m. and 18h. 58m. 

 A specially rapid movement about 19h. 19m. is referred to presently in conjunction with a corresponding 

 H change. Between 19h. 19m. and 21h. 3m. D rose, oscillating largely, 208', and the trace went off the 

 sheet on the positive side for a few minutes at the latter hour. After coming on the sheet, the D trace 

 in the course of about half an hour fell 97', rose 72', fell 75', and rose 100', going off the sheet again about 

 21h. 40m. Its reappearance a few minutes later is not very clearly shown, and at 22h. 8m. it disappeared, 

 to be seen no more before the sheet was removed at 23h. 13m. 



