COMPARISON OF ARCTIC AND ANTARCTIC DISTURBANCES. 259 



during the time when BiRKELAND's "polar" storm was largest, and during the time of his largest 

 " equatorial " disturbance. There is, however, no sign of intermission in the disturbance, though the 

 evidence is not complete owing to failure of the trace. 



Later in the 30th, it may bo added, after the time covered by Plate VI, there was a very prominent 

 bay in the Antarctic D curve, extending from about 8h. 20m. to 9h. 33m. It included a fall of 142' 

 and rise of 115'. This disturbance was at least an approach to the "special type," V oscillating about 

 a mean position during the fall of D, and rising about 30y during the rise of D. There was a synchronous 

 bay on the H curve, but details are lacking, as the trace was off the sheet most of the time. 



16. October 31 to November 1, 1902 (hours 6-2, Plate VII). 



Of this "compound" storm BiRKELAND says, p. 230, "It appears at the poles with tremendous violence, 

 although perhaps its strength is even more unusual at the equatorial stations. Considering its long 

 duration and its universal distribution, we may say that it is the greatest storm that has been observed by 

 us." He regards the disturbance as consisting of a long storm lasting from about 9h. on the 31st to 3h. 

 on Nov. 1, with two, if not more, " intermediate " storms. 



Referring to his first eight charts, which answer to times from 9h. Om. to 12h. 30m. on October 31, 

 he says, p. 232, that the equatorial stations show " powerful perturbing forces directed southwards," the 

 forces at Dehra Dun and Batavia being almost double those in central and southern Europe. During this 

 time BIRKELAND'S Arctic stations showed no very large disturbances, but Sitka was highly disturbed. 



Charts IX, X, and XI, for 13h. 30m., 13h. 42m., and 14h. Om., represent the conditions during the 

 "first powerful intermediate storm," whose maximum is put at 13h. 42m. This includes the time of 

 largest movements at the polar and equatorial stations. There are also movements at all the non-polar 

 European stations, but these are on the whole smaller than the movements later in the day. 



After 14h. Om. conditions were everywhere less disturbed for some hours. But from 17h. 45m. 

 to Ih. Om. on Nov. 1 there were further large disturbances in the Arctic and the European stations, 

 which are dealt with in BIRKELAND'S Charts XII to XIX. 



The second "intermediate" storm is regarded as extending from 23h. 12m. to Oh. 42m. on Nov. 1, 

 with maximum about 23h. 45m., and after its conclusion the conditions became much quieter. 



As usual, Kew seems to be fairly representative of non-polar European stations. It is very difficult 

 there to assign even an approximate time for the commencement of the disturbance. One has to go back 

 to 20h. on the 30th to get a time really free from the small undulatory movements which represent the 

 disturbance up to noon on the 31st. The end of the disturbance between 3 and 4 a.m. on Nov. 1 is 

 more definite. The Kew D curve shows two slow wave-like movements in immediate sequence, extending 

 from 7h. 30m. to lOh. Om. on the 31st, the rise and fall in each being from 1' to 2'. From llh. 40m. 

 to 14h. 30m. there was another group of movements of a more irregular character, which included a fall 

 of 4' and rise of 3' between 13h. 20m. and 13h. 50m. This corresponds to BIRKELAND'S first "inter- 

 mediate " storm. 



From 17h. on the 31st to 2h. on Nov. 1 there was considerably more disturbance at Kew than earlier. 

 Between 17h. Om. and 17h. 48m. D fell and rose 3', reaching a sharp peak at the latter hour. After 

 17h. 48m. D continued to fall generally, with minor oscillations, until 22h. 10m., the fall in this time 

 amounting to 13'. D then rose 4' - 3 in two steps to a rounded peak at 23h. 10m. Between this hour and 

 Oh. -15m. on Nov. 1 it fell 6' and rose 7' ; the turning-point, which was the minimum during the disturbance, 

 was at about 23h. 42m. 



In the Kew H curve the most rapid changes were a fall of 26y and rise of 23y between 13h. 15m. and 

 13h. 42m. corresponding to BIRKELAND'S first "intermediate" storm and a fall of 25y between 

 17h. 45m. and 17h. 53m. There was a comparatively quiet time from 1-th. 40m. to 17h. 45m. After the 

 latter hour there was no cessation of disturbance until about 2h. on Nov. 1. 



In the Antarctic a highly disturbed state of matters existed from about 8h. 50m. to 14h. Om. on 

 the 31st. The phenomena resembled four disturbances of the " special type," following one after the other 

 without any interlude ; but D and V were not quite in phase, and most of the turning-points on the 

 H trace were beyond the limits of registration, so one can only see that this element was approximately 

 in phase with V. 



2 L 2 



