160 



RECORDS OF DISTURBANCES 



stations, it will ho remembered, the notable feature at the commencement was the rise in the Horizontal 

 Force. In the Antarctic the Horizontal-Force trace whose sensitiveness is nearly four times that of the 

 corresponding traces at Falmouth and Oolaba shows, at first, only the most trifling of movements. It is 

 the D curve which is the disturbed one. This shows a very marked <l<nill? movement. There is first an 

 increase in I' (/'.<. movement down the sheet), commencing at 11.6 p.m., L.T. (11.59 a.m., G.M.T.), and 

 lasting about 4 minutes. This answered, apparently, to the increase in the Kew and Falmouth H curves 

 from the commencement up to the time when the curves show a temporary arrest in the movement. 

 Following this, however, is a larger swing in the opposite direction. The second summit was not reached 

 until 2 or 3 minutes after the conclusion of the increase in H at the co-operating stations, but the move- 

 ment during the last 3 minutes of the movement was small. The peculiar nature of the Antarctic 

 phenomena is, perhaps, best brought out by contrasting the changes which occurred there during the 

 two portions of the double movement, from 11.59 a.m. to 12.9, G.M.T., with those which occurred 

 synchronously at Kew. 



At the co-operating stations, movements from 2.10 to 2.28 p.m., G.M.T., and from 7.4 to 7.11 p.m., 

 G.M.T., were fairly identifiable. In the Antarctic there are fairly recognisable turning- or stopping-points 

 at 2.10 and 2.28 p.m., G.M.T., in all the elements, and a comparison was made between the changes of 

 force at the various stations during these 18 minutes, the results of which are given afterwards. It 

 should be noticed, however, that whilst 2.10 p.m. (1.17 a.m., L.T.) is a peak, and 2.28 p.m. a prominent 

 hollow, there is an intervening peak at 2.20 p.m. (1.27 a.m., L.T.), so that in the Antarctic the change from 

 2.10 to 2.28 p.m., G.M.T., was not persistent in one direction. 



Owing, presumably, to the rapidity of the movements, the Antarctic D trace became invisible during 

 several minutes both before and after 7. 11 p.m., G.M.T., so what happened from 7.4 to 7.11 p.m. in that 

 element is uncertain. The largest of the recorded D and H movements took place between 4.25 and 

 5.50 p.m., G.M.T. (3.32 and 4.57 a.m., L.T.), whilst the largest V movements took place between 6.51 

 and 7.30 p.m., G.M.T. (5.58 and 6.37 a.m., L.T.). These were also the times when the largest movements 

 occurred at the co-operating stations. 



65. Plate XXIII shows what was, on the whole, a very quiet state of matters for the Antarctic. Its 

 interest lies in the fact that the prominent oscillation in the D curve, which took place between 8 and 

 9 a.m., L.T., on August 21, synchronises apparently with the sudden change in H at the co-operating 

 stations shown in the top curves of Plate XV. Whilst there can be little doubt that the movement in the 

 Antarctic is due to the same source as the commencing movement at the co-operating stations, there is a 

 doubt as to what corresponds to what. At all the co-operating stations H showed a sudden rise, 

 commencing at from 9.6 to 9.7 p.m., G.M.T., on August 20, and continuing until 9.10 p.m. Before 

 9.6 p.m. the curves were very quiet. After 9.10 p.m. H diminished, but only very slowly. In the 

 Antarctic the D curve shows a sudden movement up the sheet which lasts 4 minutes, but it seems to 

 commence at 8.10 a.m., L.T. (9.3 p.m., G.M.T.), and it is immediately followed by a reverse swing of larger 

 magnitude also lasting 4 minutes. This, in its turn, is followed after a minor oscillation by a move- 

 ment up the sheet, bringing the D trace back to the position it occupied originally. The V curve shows 

 an obvious double movement, but the first obvious movement (down the sheet, or decreasing force) 

 sychronises with the second, not the first movement in D, and the second, or upward, movement follows 

 thereafter. 



However, on looking closely at the Antarctic V curve, it will be seen that its trend during the 

 4 minutes preceding the downward movement commencing at 8.13 or 8.14 a.m., L.T., is not quite in a line 



