COMPARISON OF ARCTIC AND ANTARCTIC DISTURBANCE. 263 



ly or 2y, and this is followed by a rise of about 7y in the course of the next 6 or 7 minutes. There 

 were peaks on the D curve at 5h. 41m. and 5h. 45m. Between these two times D rose 7', and during the 

 next 9 minutes it fell II', There was also a peak on the H trace at about 5h. 41m., the next turning- 

 point being about 5h. 51m. ; in the interval H rose 20y. These movements in the D and H curves are, 

 however, not conspicuously different either in size or rapidity from a good many others, and the apparent 

 coincidence in time may be accidental, 



One would hardly describe the Antarctic curves as disturbed until after IGh. From then until 23h. the 

 disturbance was continuous and very considerable. During the time covered by Plate IX the largest 

 movements recorded in D were a fall of 156' between IGh. 44m. and 17h. 13m., followed by a rise of 213' 

 between 17h. 13m. and 17h. 33m. The II trace was mostly off the sheet after 15h. V, however, showed 

 some considerable movements, rising 79y between 17h. 10m. and 17h. 35m., falling 62y between I7h. 37m. 

 and 17h. 46m., then rising 38y between 17h. 46m. and 17h. 57m., and falling 80y between 17h. 57m. and 

 18h. 17m. This last movement, however, extends beyond BIRKELAND'S period. 



The Antarctic movements after 16h. 47m. are shown in the right-hand figure of our Plate XL. In it 

 4 a.m., December 10, answers to 16h. 53m., G.M.T., on the 9th. This figure shows the Antarctic 

 disturbance for more than an hour subsequent to the time covered by BIRKELAND'S Plate IX. The 

 movements which it shows, though large, are if anything inferior in size to some recorded between hours 

 20 and 22, G.M.T., i.e. about two hours later. The disturbed conditions continued until nearly 23h. 

 One might thus be inclined to infer that the Antarctic storm, while so far synchronous with that observed 

 in the Arctic and elsewhere after 16h., continued long after the disturbance elsewhere had ceased. The 

 D and H Kew curves show, however, between 19h. and 22h., some movements which, though less than 

 those between IGh. and 18h., are larger than those occurring between 5h. and 7h. It would be of interest 

 to know what was happening in the Arctic between 18h. and 22h. 



19. December 14-15, 1902 (hours 23-5, Chart X). 



This " elementary polar " storm is described by BIRKELAND, p. 87, as appearing " upon an otherwise 

 very calm day .... without any preceding equatorial perturbation," and as consisting of " a great storm 

 in the north, about Dyrafjord and Axcloen .... accompanied by a perturbation, small indeed, but well 

 defined, .... observed in Northern America and Europe." 



The effect is described as "just perceptible" at Dehra Dun, but not visible at Batavia. At Dyrafjord, 

 where the movement was largest, the storm is said to have lasted from Oh. 10m. to 3h. 15m., the 

 maximum value of the disturbing force, 386y, being met with about Ih. 8m. At AxelSen, where the 

 maximum disturbing force was about half that at Dyrafjord, the times were somewhat later, the maximum 

 not appearing until Ih. 46m. In temperate Europe the disturbance is said to begin " rather suddenly 

 at Oh. 45m." and to last about 3 hours. BIRKELAND adds, " This perturbation .... has its origin in 

 the northern regions. Its sphere of action .... is concentrated about the neighbourhood of Dyrafjord 

 and Axeloen. The shortness of its duration, as also the comparatively calm character of the curves .... 

 seems to indicate that this is a polar elementary storm of the most typical nature ; it appears to be produced 

 by a coherent impulse, which increases to a certain size, and then again decreases to .... At the same 

 time, as the perturbation does not make its appearance at all places simultaneously, the perturbing cause 

 must be supposed to move with a somewhat continuous motion," p. 87. This remark has been quoted 

 at length, because in several respects it is so suggestive of the Antarctic " special type " of disturbance, 

 the principal difference being that the value of V in the Antarctic usually remained elevated for some 

 time after the apparent end of the disturbance in D and H. 



In Europe, as BIRKELAND says, the disturbance was small outside the Arctic. At Kew, for instance, 

 H rose about lOy between Oh. 45m. and Ih. 5m. and then fell very gradually until about 2h. 40m., 

 the total fall being about 15y. D rose about 2' -9 between Oh. 45m. and Ih. 5m. and then fell about 

 3' 5 to a badly defined minimum about 2h. 5m. 



In the Antarctic there were some rather striking movements about three hours before the earliest time 

 on Plate X, and one would put the commencement of the disturbances there at about 18h. 30m. on the 

 14th. There were, however, very sudden movements commencing about 23h. 5m. in both D and H, 

 consisting of a rise and fall occupying in all some six minutes. II rose 22y and fell 34y. The D oscillation 



