274 COMPARISON OF ARCTIC AND ANTARCTIC DISTI RHANTKS. 



be said to commence, and Oh. 16m., when the trace went off the sheet, H rose 54y ; between Ih. 7m. and 

 Ih. 42m. it fell 42y. Between Ih. 42m. and 2h. 12m. H rose 42y, again going off the sheet, but only for 

 about a minute. 



After 2h. 10m. the Antarctic curves were quiet, according to the Antarctic standard. 



The large D and H movements observed in the Antarctic after 23h. 30m. on the 30th synchronise with 

 BIRKELAND'S " elementary polar " storm. It is impossible to decide from the form of the curve alone 

 at what instant D was really most remote from the normal, but this would seem to have been at the 

 turning-point at Oh. 56m., when the maximum for the day occurred. This answers practically to noon, L.T., 

 thus rendering possible a comparison with mean results for that hour from adjacent days. Taking a mean 

 from the five previous days we deduce an excess on the 31st of 110', answering to about 200y in force. 

 The simultaneous value of H was also substantially in excess of the normal, but how much it is impossible 

 to say, as the trace was off the sheet and very steep both when going off and coming on. Probably the 

 maximum value of the horizontal component of the disturbing force in the Antarctic, measured after 

 BIRKELAND'S method, was fairly similar to that at Axeloen, 280y, or, say, half that at his most disturbed 

 station, Dyrafjord. The disturbance of March 30-31, regarded from an Antarctic standpoint, was, of 

 course, by no means a large one. 



30. The intercomparison of the Antarctic curves with BIRKELAND'S records points to the following 

 conclusions : 



1. At the times of the small sudden movements which BIRKELAND assigns to "equatorial perturbations" 

 there seem to be almost always (no certain exception has been noted) corresponding movements in the 

 Antarctic. The Antarctic movements are larger, usually much larger, than those recorded at the 

 equatorial or non-polar stations, and are usually, if not always, oscillatory in type. 



2. At the times of BIRKELAND'S " elementary polar " storms in the Arctic, the conditions in the 

 Antarctic are generally more than usually disturbed. The times of the largest movements in the Antarctic 

 usually occur not far from the times of maximum disturbance in the Arctic. Not infrequently, however, 

 the disturbances in the Antarctic continue without any marked subsidence of intensity throughout times 

 which BIRKELAND regards as including two or more elementary polar storms. 



3. In the Antarctic, the sudden commencing movements which BIRKELAND assigns to equatorial 

 perturbations are sometimes immediately followed by disturbances which are not separated by any 

 markedly quiet interlude from subsequent disturbances which synchronise with Arctic disturbances which 

 BIRKELAND believes of the " elementary polar" type. 



4. The "elementary polar" disturbances of BIRKELAND seem practically all confined to the hours 

 13 to 2, G.M.T. (or a.m. to 1 p.m., Antarctic L.T.), and so occur at a time when the Antarctic movements 

 are usually of a rapidly oscillatory character, and avoid the hours when the rounded wave-like movements 

 of the " special type " are usually found. 



Further, BIRKELAND'S results are limited to the Antarctic Summer, i.e. to the season at which few if 

 any disturbances of the " special type " were recorded. 



It would clearly be of great interest to know what was the nature of the phenomena in the Arctic 

 during the times of occurrence of the Antarctic "special type "of disturbance; also whether the Arctic 

 stations show a marked diurnal variation in the type of disturbance corresponding to that seen in the 

 Antarctic. 



One of the results of the comparison has been to make me realise even more clearly than before the 

 desirability of much reduced sensitiveness in magnetographs intended for use in polar regions. It is clear 

 that most fundamentally important results might be hoped for if simultaneous complete records were 

 obtainable from a series of stations in the Arctic and Antarctic regions so situated that the effects of day 

 and night could be adequately brought out. This comparison should extend over a complete year, so as 

 to bring out seasonal effects. 



