392 



NATURE 



\_Mar. 14, 1872 



AURORA AUSTRALIS 

 C\^ SutiJaythe 4th instaint, at gh. 28m. p.m., my attention 

 ^-^ was suddenly called to a " fire." Looking in the di- 

 rection indicated, I saw at S.S E., about 15° above 

 the horizon, a glare of reddish light. Curious to know 

 whereabout the supposed fire was, I kept iny eyes upon that part 

 of the heavens. Presently, similar pitches of light broke out on 

 either side of the first, and in a few seconds I could see, on the 

 assumption made, that there must be several fires blazing away 

 over a wide range, for the sky was here and there lit up with a 

 peculiar dark red light over an extent of at least 70° of the horizon. 

 My attention being now aroused, I had recourse to various con- 

 jectures, which w.;re speeddy abandined. The idea of an 

 aurora had occurred almost at the ou'set ; but as I had never, 

 wi'.h certainty, seea one in Mxuri'.ius ani never heard or read 

 of any having been observed there by others, I felt some reluc- 

 tance to admit the fact that I was actually witnessing one My 

 doub's, however, were soon dispelled I noti-ed that patches of 

 cloud floating across the illuminated p )rtion> of the sky reflected 

 no light, and on one or two occasions, a faint flickering, 

 like lightning, was seen a-nmg th? upper cirrus clouds. 

 Thes: ani other facts, coupled with the knowledge that the 

 mignets hid been occasioniUy distur)ed to a cons'derable 

 ex'ent on Fridiyand Saturdiy, and oa the morning of Sunday, 

 left no doubt on my mind. 



I listening to the house, I imnadiately mounted a portable 

 inclinometer and declinome'er, and took all the measures I could 

 to observe whit might take place, dividing my time and attention 

 betweei the instruments, which I put up in a verandah facing 

 the south, and the aurora right in front of me. 



The needle of the inclinometer did not give the slightest indi- 

 cUioa of adiiturbance, but the declinometer magnet was affec':ed 

 to the extent at times of 9'. 



It was gh. 4Sm., or 20m. after I saw the luminosity supposed 

 to have been caused by a fire, that I began to observe the 

 aurora systemat cally, and I append a copy of the notes which 

 I took from that time up to ih. 20m. a.m. 



What stiu:k me particularly was the apparent quietness of 

 the whole scene. Unlike the " merry dancers," which I have 

 often seen and admired in Scotland, rapidly changing shape 

 and colour, and rushing in variegated columns and bands in 

 different directions with great velocity, thereby conveying an 

 impression of energy and violence, the display of Sunday night 

 was calm and serene, giving one an idea of peace and repose. 

 Except shortly after I first saw the phenomenon, I could not 

 make out any motion of the arches, segments, or luminous bands. 

 They appeared and disappeared without change of locality, the 

 intensity of the light increasing or decreasing without any 

 flickering. I coull see no shooting, darting, or rushing of the 

 bands or beams. Each made its appearance and disappearance 

 simultaneously along its whole length, as if the action was 

 vertical. 



The spectacle presented by the beams from 11 r. M to 1 1 . 20 

 P.M. was at once grand and lovely beyond description. Almost 

 from the extreme left to the extreme right, and from as low down 

 as I could see up to a meridional altitude of ab:>ut 72^% the sky 

 was furrowed with alternate white and dark bands, all of which, 

 so far as I could judge, were parallel to each other and to the 

 magnetic meridian. They were generally at unequal intervals, 

 sometimes crowded together, and sometimes considerably apart ; 

 but in this respect I could only judge of those near the meridian. 

 At times they presented the appearance of graceful folds and 

 convolutions, but the action seems to have been performed so 

 gently and imperceptibly as to convey no idea of motion. They 

 presented the same colour during the whole time, namely, a steel 

 grey to a silver white. 



The arches and segments were of a blood, cherry, or Indian 

 red, and every now and then, when the intensity of the light in- 

 creased, the stars twinkled like gems seen through a delicate pink 

 curtain or veil placed before them. Occasionally one could fancy 

 that he was looking at the Southern Cross through very trans- 

 pirent glass or crystal of an exquisite ruby tint into an inner 

 chamber lit up with light of a similar colour. 



The light was never very strong. I saw no part of the land- 

 scape lighted up by reflection. It is to be borne in mind, how- 

 ever, that I was occupied with the instruments, and that much 

 may have escaped my attention. 



During some parts of the night black clouds passed over the 

 field of view, and I believe, although I could not see them, ex- 

 cept on one or two occasions, that they were light cirrus and 



cirro-stratus clouds in the upper regions, as hai been the case 

 throughout the day. 



The wind was light from E. by S. throughout, and the 

 barometer was 'too inch below the mean for the season. 



After I A.M. the aurora speedily died away. At 3 A.M. I could 

 see nothing ; but looking out at 4.30 .\.M. I saw a red glow in 

 the southward, wliich at first I took for aurora, but which turned 

 out to be cirrus clouds lit up in the early dawn. 



Throughout Monday the magnets were quiet. A great many 

 cirri appeared, which, in the evening, assumed at eastward and 

 westward a dark red colour, very much resembling that of the 

 aurora. 



The Magnetic Observatory, which had barely commenced 

 operations, may be said to have been inaugurated on Sunlay 

 night, an 1 it is possible that its future records will show, amongst 

 other things, that aurora is not so unfrequent in Mauritius as is 

 supposed, although such a displiy as that which has just occurre 1 

 may not be seen for many years to come. In the end of August 

 and beginning of .Septe nber, 1S59, aurora was observed over a 

 considerable portion of both hemispheres, and oa one night 

 during that period I siw a reddish glo* in our southern sky, 

 which may have been the Aurora Australis. Probably the 

 present display has been seen over a great part of the globe. 

 Has any unusuil solar activity been observed? Oa Friday a 

 chain of spots stretched over nearly the whole of the sun's disc, 

 and a large group occupied another part of it. On Monday the 

 chain had disappeared. Any one who may have made observa- 

 tions in 'he colony or at s-a on Suniiv night would oblige me 

 by sending them to the Observatory. It would be interesting to 

 know the height of the aurora. 



Aurora Australis seen at Mauritius on the \th tn ^th 

 February, 1S72. 



9. 48 p.M — An irregular convex arch of dark red light ex- 

 tending over about 60° of the horizon, an 1 having its vertex in 

 the line of the magaetic meridian. Brighe.t below the Southern 

 Cross. 



9.58 P.M. — Kn arch of a dark red colour having a cord of 

 about 70°. Vertex in or near the magnetic meridiin. Patches 

 of black cloud passing over the coloured segment fron E. by S., 

 but they reflect no light. 



to. I P.M. — -The segment is of a more intense dark red colour. 

 Its eastern limit is about 3° east of the Cross, and its brightest 

 portion from 1° to 2" above the Cross. It is broken off tosvards 

 the west, and extends in that direction to about only S. by W. 



10 4 p.M — No segment now seen, but patches of Indian or 

 cherry red on either side of the magnetic meridian at a distance 

 of 30' to 40° from it. 



10.5 P.M. — The whole has almost disappeared. 



10.19 P-^'- — An intense blood-red patch atS.S. E. having its 

 centre 2° to 3° below tlie Cross. The stars shining through it 

 wiih subdued light. 



10.20 P.M. — The red light all gone, but a broad conical space 

 of an ash-grey colour, with a slight green tinge, low down on 

 the horizon, and apparently bisected by the magnetic meridian. 

 Resembling early dawn. 



10.22 P.M. — .\ dimly defined arch of a smoky red colour ex- 

 tends from about E. S.E. to S. W. by W. The height of its 

 vertex is about 40° above the horizon. 



10.24 P'^'- — All gone. 



10.25 to 10.30 P.M. — Appearing and disappearing. Some 

 faint streaks of whitish light seen low down 



10.34 P.M. — Six bands of faint whitish light near horizon at 

 S. by E. 



10 37 P.M. — A bright meteor of firsl magnitude travelled 

 slowly from a Centauri towards N. by E. It had a train of light 

 and lelt spirks behind it. Colour white with a yellow tinge. 

 The auroral bands brighter and higher. 



11 P.M. — Sixteen luminous bands of a steel grey to a silver 

 white colour, extending from as low down as I can see to within 

 20° of the zenith. The extremity of one of them is close to 

 Canopus. Light of the Great Magellan cloud enfeebled. No 

 apparent convergence of the beams ; they seem to be quite 

 parallel. 



1 1.6 P.M. — The parallel bands are still seen. They cover the 

 greater part of the hemisphere, extending (at the meridian) to 

 about 72° above the horizon. On their eastern and western ex- 

 tremes there are patches of blood-red light, but none in the in- 

 termediate space. Some of the bands appear to be folded in a 

 direction from west to east. 



II. 7 P.M. — Dying away. 



