COMPARISON OF AECTIC AND ANTARCTIC DISTURBANCES. 2G7 



On tho H trace there were some fairly large oscillations, but only partly shown. H rose 56y between 

 Ih. 13m. and Ih. 26m.; the trace was then off tho sheet for 21 minutes on the positive side. Between 

 Ih. 47m. and 2h. 31m. II fell and rose 53y, the trace again going off the sheet. Between 4h. 16m. and 

 5h. 13m. H rose 105y. 



The V trace was, on tho whole, quiet. It contained, however, a small bay from about Ih. 13m. to 

 Ih. 48m., V rising and falling about 19y. 



25. February 8, 1903 (hours 8-12, Plate XVI; and hours 13-24, Plate XVII). 



Before discussing this disturbance BIRKELAND mentions, p. 187, that conditions in the Arctic had been 

 on the whole very quiet since the end of November, 1902, until February 7, 1903. On that day, he says, 

 a fairly powerful storm was experienced in the Arctic from 21h. 5m. on the 7th until about Ih. on the 28th. 

 There was, I may add, also marked disturbance in the Antarctic at the same time, but it commenced 

 earlier, about 19h. 30m. on the 7th. 



Tho disturbance of February '8 is classed amongst the "compound." It is regarded as divisible into 

 three sections, the first of which covers the time to which Plate XVI refers. As this section is allowed a 

 separate plate, and there is a gap of an hour between the times represented by the two plates, I shall treat 

 the two parts separately. During his Section (i) BIRKELAND remarks, p. 187, that "The perturbation is 

 particularly powerful at Sitka, and is (there) especially violent from 9h. to 9h. 35m." It continued to be 

 considerable at Sitka until llh., but ran a rather irregular course there and at the Arctic stations. 

 BIRKELAND adds, p. 188, " The simple conditions found between San Fernando in the west and Zi-ka-wci 

 in the east, and between Kew in the north and Batavia in the south, form a strong contrast . . . the 

 perturbation is throughout chiefly in H. It is well defined, and, as far as we can determine, commences 

 everywhere simultaneously at about iSh. 35m. ... It terminates simultaneously at about lOh. 50m." The 

 time of maximum at the co-operating stations outside North America is given as from lOh. Om. to lOh. 10m. 



BIRKELAND, p. 189, considers that the phenomena at tho American stations suggest "a polar elementary 

 storm, at first not very far north-east of Sitka," but this could not, he says, account for the phenomena 

 " over the district between Kew and Batavia," which suggest a " negative equatorial storm," i.e. a 

 disturbance due " to a current round the PLirth from east to west ... at a distance from the Earth of at 

 least a magnitude equal to the radius of the Earth." If I rightly follow him, the view he finally inclines 

 to, p. 189, is "that at first the perturbation partakes most of the nature of a cyclo-median storm, and 

 subsequently changes into a more purely polar one." 



At the non-polar European stations the phenomena were similar to those at Kew. There H fell 

 gradually about 40y between 8h. 35m. and lOh. Om., and then rose 30y between lOh. Om. and lOh. 50m. 

 For some reason which I do not understand, BIRKELAND, p. 188, regards this as the end of the storm at 

 Kew, and elsewhere, during his Section (i). But as a matter of fact the Kew H curve began to fall again 

 slightly immediately after lOh. 50m., and between llh. 20m. and llh. 50m. it rose 17y, falling 14y 

 during the next 30 minutes. The trace was quieter for a short time after 12h. 20m. The D trace at 

 Kew showed a rise of from 2' to 2' - 5 above the normal between 9h. 30m. and lOh. 40m. D was, if 

 anything, falling at lOh. 50m., the normal change at that hour being a rise. Decidedly the most 

 conspicuous movement was a rise of 4' -8 between llh. 35m. and llh. 55m. There was a fall of 3' 5 

 between 12h. Om. and 12h. 40m. 



In the Antarctic the working of the V magnet appears doubtful. The H trace was off the sheet on the 

 positive side, except during a few minutes, until 8h. 56m. Between 9h. 38m. and lOh. 39m. the trace 

 shows a prominent to-and-fro movement a fall followed by a rise strongly suggestive of the special 

 type of disturbance. The full extent of the movement is not shown, as the trace was beyond the limits of 

 registration on the negative side for some 15 minutes, but the amplitude exceeded 68y. The turning- 

 point, a minimum, must have occurred within a few minutes of lOh. Om. The D trace was off the sheet 

 at this time on the negative side, having been off since about 8h. 10m., and did not appear until lOh. 53m. 

 It went off and came on steeply, suggesting a deep bay or bays. 



Between lOh. 53m. and llh. 33m. D rose 82'. Between llh. 33m. and 12h. 25m. it executed a to-and- 

 fro movement, somewhat suggestive of the special type of disturbance, a fall exceeding 82' being followed 

 by a rise of over 1Q5'. The trace was off the sheet only for a minute or two, the turning-point coming at 



2 M 2 



