COMPARISON OF ARCTIC AND ANTARCTIC DISTURBANCES. 257 



table, p. 222, the first "intermediate " storm commenced about 18h. 10m. and ended about 19h. 30m. 

 at most European stations, the maximum coming about 18h. 45m. The value of PI the maximum 

 horizontal disturbing force varied from 248y at Axeloen to 3y at Toronto, the value at Kew, 16y, being 

 slightly under the average for non-polar European stations. 



The time of commencement of the second "intermediate" storm is given as about 21h. 30m. at most 

 stations, but somewhat curlier in the Arctic. The end is given as usually somewhat after 23h. The 

 maximum is said to have occurred about 22h. 10m., the value of P! varying from 266y at Axeloen 

 to 2-5y at Batavia. The value given for Kew, IG'Sy, is again slightly below the mean for non- Arctic 

 Europe. 



The disturbances outside the Arctic were really very trifling. The most notable change at Kew was 

 a rise of 20y in H between 21h. 30m. and 21h. 48m. 



In the Antarctic there was no loss of V-traco during the time covered by Plate V, except from 

 22h. 43m. to 23h. 13m., when there was no sheet on the drum, and the H trace was off the sheet only 

 for a short time before the end. The D trace, however, was off the sheet a good deal between 20h. and 

 22h. 43m. 



The largest D movements recorded took place between 19h. 10m. and 19h. 58m., and so synchronise 

 with or overlap the latter part of BIRKELAND'S first " intermediate " storm. During this time D rose 

 41', fell 28', rose 45'+ (going off the sheet), fell 52' + , and rose 50'. 



Some rather notable oscillations also occurred in H. The element rose 37y and fell 53y between 

 18h. 38m. and 19h. Om., the turning point (a maximum) being at 18h. 50m. and so practically 

 simultaneous with the maximum in BIRKELAND'S first " intermediate " storm. Another considerable 

 oscillation took place between 19h. 40m. and 20h. 10m., H first rising 55y and then falling 52y. The 

 V trace showed numerous small oscillations. There was one rather sharp oscillation between 20h. 5m. 

 and 20h. 16m., a fall of 19y being followed by a rise of 18y. The intervening minimum occurred at 

 20h. 9m. Between this hour and 21h. 20m. there was a total rise of 36y in V, which was followed 

 during the next 20 minutes by a fall of 27y. 



The D trace went off the sheet rather steeply at 21h. 45m., and came on rather steeply at 22h. 25m., 

 so there may have been a considerable oscillation in this element during the time of BIRKELAND'S second 

 "intermediate" storm. The H and V traces, however, after 21h. 40m. were quieter than they had 

 been for some hours previously. Thus whilst there was decidedly more than the average amount of 

 disturbance in the Antarctic during BIRKELAND'S first " intermediate " storm, it is at least doubtful whether 

 the same was true of the second " intermediate " storm. 



15. October 29-30, 1902 (hours 16-4, Plate VI). 



This "compound" perturbation is said, p. 161, to consist of an "equatorial" perturbation which 

 commenced suddenly on the 29th at 16h. 52m., and whose most active phase in the southern stations 

 appeared at about Ih. 30m. on the 30th and of " polar" storms. Whether BIRKELAND supposed the same 

 equatorial perturbation to last continuously all the time is not clear. As to the nature of the coincidence 

 of the equatorial and polar disturbances, p. 161 says: "The positive equatorial perturbations observed 

 by us are always accompanied by polar storms. As a rule, the polar storms do not begin until a little 

 while after the equatorial ; but on this occasion they begin almost simultaneously. . . ." 



In discussing his Chart I, which includes results for hours 18h. 52 -5m. and 20h. 30m. on the 29th, 

 BIRKELAND concludes, p. 164, that " it is the polar systems that give the field its character," and he puts 

 the " centre " of the polar system near Matotchkin Schar. In discussing Chart II for Ih. Om. on the 30th, 

 he regards the field as " now mainly conditioned by the equatorial perturbation." 



During the major part of the polar storm BIRKELAND had records from only two polar stations, Axeloen 

 and Matotchkin Schar. The largest movements shown at either occur between 18h. and 21h. 



At the non-polar stations there was a distinct sudden commencement not clearly apparent at the polar 

 stations whose time of occurrence BIRKELAND puts at 16h. 52m. The original Kew H trace shows a 

 small fall, about ly, between 16h. 52m. and 16h. 54m., followed by a rise of about 4y during the next 

 4 minutes. 



The most noteworthy movement at Kew and the other non-polar stations took place between 1 and 



2 L 



