COMPARISON OF ARCTIC AND ANTARCTIC DISTURBANCE 



253 



'I'll is case is a good example of the uncertainties attending the application of liuiKKi.ANu's method to 

 the Antarctic curves, even under the most favourable conditions. From inspection of the adjacent portions 

 of trace one would conclude that D and V were normal, Imt II distinctly below the normal value from 

 1-th. 13m. to 15h. Om. If, however, wo compare the values of the elements at 14h. 53m. (otherwise 

 2 a.m., L.T., on October 7) with the means for the same hour from the four nearest days, this ia what we 

 find : 



These figures point to exactly the opposite conclusion to that suggested by the form of the curves 

 themselves. 



11. October 11-12, 1902 (hours 12-2, Plate II). 



This '-compound" perturbation is regarded by BiRKELAND, p. 251, as divisible into three so-called 

 "sections," (i) from llh. to 17h. 20m., and (ii) from 17h. 20m. to 18h. 30m. on October 11, (iii) from 

 the last-mentioned hour to Oh. 30m. on the 12th. 



The disturbance in section (i) is regarded as " mainly a positive equatorial perturbation," accompanied, 

 however, from 12h. 25m. to 13h. 15m. by a "considerable polar perturbation." "The farther we go," 

 BIKKELAND says, p. 252, "from the (N.) polar regions, the less perceptible does this brief polar perturbation 

 become .... At Zi-ka-wei and Dehra Dun it is distinctly noticed, at Batavia it is almost imperceptible. 

 At Christchurch, on the other hand, there is a rather violent perturbation .... (which) cannot have 

 been produced by the same system .... for the effect of the latter is imperceptible (?) even at Honolulu 

 and Batavia. The explanation of this seems to be that simultaneously with the descent (of ions or 

 corpuscles) in the north, a similar phenomenon appears near the South Pole, and it is the effects of the 

 latter that we observe at Christchurch." 



This quotation has been given at length because it constitutes one of the very few references which 

 I have observed to the possible existence of disturbance centres near the S-pole. The "explanation" 

 was presumably purely a hypothesis on BIRKELAND'S part, as he had no records from south of Christ- 

 church. 



Section (ii), 17h. 20m. to 18h. 30m., was characterised by "violent storms in the Arctic," especially at 

 Matotchkin Schar, but " the effect of the equatorial storm is still perceptible." 



Section (iii), 18h. 30m. to Oh. 30m., "is characterised by a long polar storm," in the course of which, 

 however, there appeared three short " intermediate " polar storms, the first with maximum about 18h. 34m., 

 the second lasting from 20h. 45m. to 21h. 20m., the third from 23h. 10m. to Oh. 25m. 



At Kew and all the other non-polar stations whose curves appear in Plate II there was a fairly sudden 

 commencing movement, which does not seem to be mentioned by BIRKELAND. The H movement at Kew 

 commenced about 12h. 18m., a fall of 2y and a rise of lOy occurring in about 6 minutes. A peak, 

 representing a movement of about 1' to the west, appeared also in the Kew D curve at about 12h. 24m., 

 i.e. simultaneously with the maximum in H. Plate II shows this commencing movement distinctly at 

 Colaba, Batavia, and Christchurch. It forms in fact the commencement of the movement at Christchurch, 

 which BIRKELAND suggests may be due to currents near the S-pole. 



At Kew and the other non-polar stations the disturbance consists mainly of bays in the H and D curves, 

 with two or three small but fairly sharp peaks, the greatest departures from the normal appearing between 

 17h. and 22h. Christchurch differs a little from the other non-polar stations in that there is a bay 

 on the H curve between 12h. 18m. and 14h. 10m., which commences less suddenly, but is larger than 

 those encountered elsewhere ; the later movements at Christchurch, on the other hand, are exceptionally 

 small. The division into three sections seems somewhat arbitrary, especially the line of demarcation 

 drawn at 18h. 30m. between Sections (ii) and (iii). This comes in the middle of a very rapid rise 





