258 COMPARISON OF ARCTIC AND ANTARCTIC DISTURBANCES. 



2 a.m. on the 30th, the maximum displacement being that already referred to as occurring about Ih. 30m. 

 The disturbance at this hour appears to have been a good deal larger at Dehra Dun, Data via, and Christ- 

 church than at the non-polar European stations, BIRKELAND'S estimate of the horizontal disturbing force 

 being 43y at Batavia and 40y at Christchurch, as against 14y at Kew. 



In the Antarctic there was an outstandingly rapid rise of H from about 16h. 55m. to 16h. 59m., followed 

 by an equally rapid and larger fall. The trace was very faint near the time of the turning-point, and got 

 beyond the range of registration at 17h. 5m., so that all one can be sure of is that between 16h. 55m. and 

 17h. 5m. H rose at least 27y, and fell at least 37y. A slow rise in H commenced about 16h. 53m., but 

 this was checked for a few seconds at 16h. 55m., and the movement did not attain its highest rapidity 

 until perhaps 16h. 56m. This H movement occurred at a time when the trace had been rather quieter 

 than usual for an hour or more, and there can be little doubt that it represents the sudden commencement 

 seen at BIRKELAND'S non-polar stations. In the Antarctic, synchronous apparently with the commencing 

 movement in H, there was a sharp oscillation in V, a rise of lOy and fall of 67 taking place in about 

 6 minutes. D, which had been rising on the whole fairly steadily with minor oscillations, began a more 

 decisive though not conspicuously rapid rise about 16h. 56m. During the next 27 minutes it rose 73' 

 and the trace then got off the sheet. It came on the sheet 3 minutes later, but, after being on for about 

 18 minutes, got off once more, and thereafter was seen only at rare and short intervals during the 

 remainder of the time covered by Plate VI. 



The H trace remained beyond the limits of registration until about 19h. 18m., and was again lost sight 

 of about 19h. 45m. The light in the Antarctic magnetographs evidently became very faint towards the 

 end of the sheet, as even the base lines are but faintly indicated after 21h. The V trace, which suffered 

 less from weak illumination than the D and II traces, had become invisible by this hour. It is thus 

 possible that faintness of light may have been partly responsible for the non-appearance of the D and II 

 traces after 20h. 



The persistence, however, of active disturbances until the time when the V trace became invisible may 

 be safely inferred from the following list of observed changes in V : 



From 17h. Cm. to 17h. 48m. rise 57y, 



17h. 48m. 17h. 54m. fall 36y, 



17h. 54m. 18h. 5m. rise 33y, 



ISh. 57m. 19h. 8m. rise 38y, 



19h. 8m. 19h. 30m. fall 58y, 



19h. 30m. 19h. 45m. rise 33y, 



19h. 45m. 20h. 1m. fall 36y, 



20h. 1m. 20h. 8m. rise 30y, 



20h. 8m. 20h. 23m. fall 35y. 



The major part of these V disturbances synchronise with BIKKELAND'S " polar " storm, but some precede 

 it. Shortly after the last movement recorded above the trace became invisible. 



After the next sheet was put on at 23h. 20m., distinctly disturbed conditions existed until after 3 a.m. 

 on the 30th. The changes in. V were especially noteworthy. Between Oh. Om. and Ih. 4m. on the 30th 

 there was a rise of 92y, between Ih. 4m. and Ih. 46m. a fall of 74y, and between Ih. 46m. and 2h. 46m. a 

 rise of 93y. H rose 52y between Oh. Om. and Oh. 40m., the trace then going off the sheet on the positive 

 side. After being off for 9 minutes it came on, but 20 minutes later it went off again on the positive 

 side. Coming on once more at Ih. 36m., it showed a fall of 59y between Ih. 36m. and 2h. 17m., and a 

 rise of 59y between 2h. 17m. and 2h. 35m. The trace went off the sheet at the latter hour, and except 

 for a short appearance of about 10 minutes re-appeared no more until after Sh. 



During the above changes in V and H the chief movements in D were a fall of 129' between Ih. 10m. 

 and Ih. 43m., and a rise interrupted for 25 minutes by minor oscillations of 87' between Ih. 43m. and 

 2h. 45m. After 3h. 30m. the D and V traces were specially quiet during the next 5 hours. The H trace 

 being off the sheet, one cannot be certain that it was equally quiet. 



It will doubtless have been noticed that the largest movements recorded in the Antarctic occurred 



