April i, 1920] 



NATURE 



^n 



ments. In the course of about five minutes from 

 i7h. 8m. to i7h. 13m. there was a swing of 1° 35' 

 to the east, immediately following a somewhat less 

 rapid swing of 44' to the west. In the course of about 

 twelve minutes from ih. 9m. to ih. 21m. on March 23 

 there were swings of 76' to west and 59' to east, and 

 after a minute's pause the latter swing continued, so 

 that declination at ih. 28m., when the trace went off 

 the sheet, was 1° 35' less westerly than it had been 

 nine minutes before. The range actually shown on 

 the sheet, 2° 1', has seldom been equalled at Kew, 

 and as the trace was off the sheet for twelve minutes 

 it was probably sensibly exceeded. 



The vertical -force trace was complete, the range 

 of disturbance being about 8207. The disturbance in 

 that element was fairly normal, the value being en- 

 hanced on the afternoon of March 22 from i3h. to 

 23h., and correspondingly depressed on the morning 

 of March 23 from oh. 30m. to 7h. The times of 

 maximum and minimum were respectively about 

 i8h. 20m. on March 22 and 4h. lom. on March 23. 



The outstanding features of the disturbance were 

 the size and rapidity of the largest movements, and 

 the separation of two very highly disturbed periods 

 by a comparatively quiet interlude lasting several 

 hours. The disturbance was preceded, twenty-seven 

 days before (February 24) by a considerable, but much 

 smaller, disturbance,' which was in some respects the 

 antithesis of the later one. It lasted only about ten 

 hours, and the largest movements occurred in the 

 course of the first three hours. C. Chree. 



Kew Observatory. 



This storm was one of exceptional violence. It 

 commenced suddenly at gh. 6m. G.M.T. on March 22. 

 The H.F. magnet experienced a sharp positive move- 

 ment of 377, followed immediately by a decrease in 

 force of 417 (17IZ10-* C.G.S. unit). Similarly, the 

 D. magnet swung sharply to the west and then to the 

 east, the range being 8' of arc. 



After three oscillations on the negative side of the 

 normal, a steady rise of value commenced in the 

 H.F. magnet at loh. 26m., which lasted until 

 i9h. lom., when the spot of light began to fall steadily 

 towards the normal value of the force. The general 

 character of the movement was that of one long wave 

 with oscillations superposed upon it, the storm being 

 most violent between i6h. and igh. lom. During this 

 period the spot of light passed beyond the limits of 

 registration in a series of rapid oscillations between 

 i6h. 24m. and i6h. 30m., i6h. 46m. and i7h. 12m., 

 i7h. 54m. and i8h. 14m., i8h. 41m. and i8h. 47m., 

 and i8h. 47m. and i8h. 51m. The oscillations be- 

 came less violent and rapid after igh. 37m. At 

 23h. 5m. the spot of light had fallen to a value close 

 to that of the base line, so that the extreme range in 

 this sweep of the curve was from a value greater 

 than 5507 to 527. 



At 23h. i6m. a rapid oscillatory recovery and in- 

 crease of value took place, which attained a maxi- 

 mum of 3767 at 23h. 36m. The spot of light then 

 went off the recording drum on the negative edge, 

 crossing the base line on March 23 at oh. 24m. During 

 the next four hours it was several times beyond the 

 limits of registration on the negative side in a series of 

 rapid oscillations, in which the greatest range exceeded 

 2607. 



The extreme range in H.F. during the storm was 

 greater than 7007. This value may be compared with 

 the range on the quiet days during January and 

 February, which had a mean value of 187. 



At 4h. 20m. the spot of light returned to a positive 

 value, when a series of very rapid shiverings of the 

 needle took place, similar to those which terminated 



NO. 2631, VOL. 105] 



the violent magnetic storm of August 11-12, 1919. 

 These oscillations had a range of about 1307, and 

 lasted until 8h. 50m. This may be regarded as the 

 end of the violent storm, though the needle continued 

 to be disturbed moderately until midnight of March 25. 



The general character of a sinuous S-like curve is 

 well shown on the trace from the vertical force 

 magnet. It crossed the base line at oh. 44m. on 

 March 23. There was a very rapid oscillation of the 

 needle at ih. om. The spot of light remained below 

 the base line until 6h. om., when it gradually rose, 

 with a shivering movement of small amplitude, to its 

 normal value. On the negative side the spot of light 

 was off the recording drum from ih. 20m. to 2h. 40m. 

 and from 2h. 40m. to 4h. om. The extreme range 

 was greater than 9007, and the greatest positive value 

 was 6427. 



Corresponding to the gradual increase in force in 

 the H.F. and V.F. elements, the declination magnet 

 gradually swung to the west. The maximum disturb- 

 ance consisted of some rapid swings of the needle 

 between i6h. 24m. and i8h. 48m. The greatest of 

 these was at i7h. om., the range being 90' of arc. 



A very remarkable rapid double swing of the needle 

 occurred on March 23 at ih. 12m. The range of this 

 oscillation was 130'. This corresponds to rapid 

 oscillations in the force elements. The spot of light 

 was now, on .the whole, below the base line until 

 4h. om., when there was a rapid movement east and 

 then west between 4h. 15m. and 5h. om., with a 

 range of 120'. A series of shivering oscillatory 

 movements then supervened until the end of the 

 storm. The greatest total range in D. during the 

 storm was 160'. 



Judging from the three elements, the general move- 

 ments both in force and in direction were rising with 

 reference to the base line during the daylight hours 

 and falling during the night hours. 



The storm was coincident with the appearance of a 

 very great sun-spot group on the sun's disc which 

 appeared between March 16 and 29, and was passing 

 the central meridian on March 22-23. Its mean helio- 

 graphic latitude was —6°, and it extended from longi- 

 tude 114° to longitude 150°. It was the biggest group 

 of sun-spots observed since August, 19 17, and its disc 

 area, in units i/5oooth of the visible disc, was 34 on 

 March 22. 



It was a revival of a similar extended group of spots 

 of large area observed from Jan^uary 21 to February 3. 

 At the next rotation, February 17-27, this group ap- 

 peared as an insignificant small spot and dots amidst 

 extensive faculae. But the magnetic elements l^egan 

 to be disturbed during this second rotation of the spot- 

 group on February 16-17. 



Through the kindness of Lt.-Col. Penny, R.A.M.C, 

 the O.C. Queen Mar}'s Military Hospital. Whalley, 

 in the immediate neighbourhood of Stonyhurst Col- 

 lege, I have received the following account of the 

 aurora borealis observed by him in the early morning 

 of March 23 : — 



"On going out of doors at about 3.i.< a.m. I 

 noticed this display, but I do not know how long 

 it had been visible. It was a clear, starlight night nt 

 the time. The aurora was exceedingly fine when I 

 first saw it, the best I have ever seen. It consisted 

 of about eight broad beams of light, most of which, 

 except the extreme west and north ones, extended to 

 within 5°-io° of the zenith. The lights extended over 

 about 9o°-ioo° from approximately north-north-east "to 

 west by north. 



" The beams became pale and brilliant again several 

 times, besides constant slighter variations in intensity. 

 On two or three occasions, within about twenty 

 minutes, most of the beams, more than three-quarters, 



