November 30, 1905] 



NA TURE 



Magnetic Storms and Aurora. 

 In view of the interest recently displayed in theories 

 as to the origin of magnetic disturbances, attention may be 

 ■directed to some rather curious phenomena exhibited during 

 the magnetic storms experienced lately. Usually when a 

 magnetic element during a storm suffers a large deviation 

 in one direction it does not simply return to, but over- 

 shoots, its original value, and oscillates about its undis- 

 turbed position. If we liken the curve to the outline of 

 an island on a map, a conspicuous indentation of the 

 coast line is usually accompanied by a correspondingly 

 pronounced promontory. Whilst this is much the more 

 common phenomenon, it is by no means very unusual to 

 have, as it were, an isolated bay in an otherwise straight 

 coast line; only when this happens the "bay" seldom 

 forms a deep indentation, and the curvature of its outline 

 is seldom very great. On November 15, during the recent 

 display of aurora, a somewhat remarkable instance of a 

 nearly isolated " bay " presented itself in the declination 

 curve trace at Kew. Taking, again, the geographical 

 analogy, it resembles — as may be seen from the accom- 

 panying copy of the curve ! — a regular estuary. We have, 

 commencing at 8.53 p.m., an easterly movement, which 

 in twelve minutes reduced the declination about 32 ' , while 

 in the subsequent twenty minutes the declination increased 

 34', thus returning very nearly to the value it had half 

 an hour before. This was by no means the only movement 

 during the magnetic storm of November 15, but it was 

 far and away the most conspicuous one. Its remarkable 

 form would predispose one to attribute it to some very 

 special cause, which one would naturally associate with 

 the coexisting aurora. Curiously, however, a very similar 

 movement was experienced three days earlier, when no 

 special auroral display seems to have been noted in this 

 country, the intervening days being free from any large 

 disturbance. This earlier disturbance — a copy of which is 

 also shown — took place on November 12, also in the even- 

 ing, but nearly 25 hours earlier than that on November 15. 

 The conspicuous movement on November 12 began 

 about 6.30 p.m. The easterly movement was fully larger 

 than on November 15, being about 35';;, while the return 

 swing to the west was about 36' -5. The double move- 

 ment occupied about thirty-eight minutes, and so some- 

 what longer than on November 15, but this is chieflv due 



Mov 15. 



Abv 15 



(>h 



lO 



SVov/6 



Up-tn.- 



to the movement on November 12 beginning and ending 

 somewhat less abruptly. 



1 he total ranges of the declination disturbances on 

 November 12 and 15 were respectively about 42' and 50'. 

 1 he other elements were also disturbed, the horizontal 



1 Two days' curves — each with its base 1 

 aphic sheet ; the upper is always the earlit 



ch pho 



force range being approximately 2007 on November 12 

 and 2507 on November 15 (17 = 0-00001 C.G.S. unit). In 

 each of these horizontal force curves there was also a 

 prominent movement somewhat analogous to the above 

 movements in the declination, but not synchronous with 

 them, and with an increase of force. The horizontal force 

 movement on November 12 was the more striking, the 

 force increasing by about 1807 in thirteen minutes, and 



JVov. II. 



Nov II 



V- brry. 



Nov. 12 



73] 



W^n- 



then falling off about 1557 in the next thirteen minutes. 

 On November 15 the nearest analogous movement was 

 of a more normal character, an increase of no 7, occupy- 

 ing about ten minutes, being followed by a fall of 

 1607 in the next twenty minutes. On November 12 the 

 prominent horizontal force change was only a few minutes 

 later than the prominent declination change, but on 

 November 15 the most prominent horizontal force movement 

 preceded the prominent declination movement by about 

 i\ hours. There were considerable horizontal force move- 

 ments at the time of the prominent declination movement 

 on November 15, but they were of a more commonplace 

 character. The disturbance on November 12 commenced 

 about 9.30 a.m., terminating about midnight; that on 

 November 15 lasted much longer, starting about 3.15 p.m., 

 and continuing for about thirty hours. 



Charles Chree. 

 National Phvsical Laboratory, November 21. 



Absorption Spectra of Ultra-violet Rays by Vapour 

 and Liquids 



In connection with some letters recently published in 

 Nature (vol. lxxii. pp. 557, 630), the following note may 

 perhaps have some interest. Researches on the above 

 named subject have been made in the physical institute 

 of the University of Erlangen. Dr. Pauer (Wied. Ann., 

 lxi., p. 363, 1897) has determined for a great number of 

 substances the position of the absorption bands, and Dr. 

 Miiller (Erlangen Inaugural Dissertation, 1903, Sitzungs- 

 berichte der physikalisch-medicinischen Societal in Erlangen, 

 vol. xxxiv., p. iSS, 1902) has tried to get some values of 

 the absorption coefficients of vapours. By the researches 

 of Friedrichs and Grebe, the results of Pauer have been in 

 many respects amplified. Perhaps I may direct attention 

 to the fact that Dr. Pauer found that the law of Kundt on 

 the displacement of the absorption bands towards the red 

 with increasing refraction index or dispersion is true when 

 passing from the vapour to the liquid and then to the 

 solutions in different media. His observations were made 

 on benzol, toluol, the isomers of xylol and sethylbenzol, 

 chlorobenzol, bromobenzol, iodobenzol, anilin, nitrobenzol, 

 pyridine, bisulphide of carbon. Benzol and bisulphide of 

 carbon were especially carefully treated by him. 



Erlangen, November 13 E. Wiedemann. 



