Oct. 30, 1884] 



NA TURE 



63; 



rays which succeed in being refracted or bent round through 

 our atm isphere (the amount of bending of the light extending 

 to a maximum of about 70' in the lowest strata of the atmo- 

 sphere). Into this inner circle, in this case about 2525 miles in 

 diameter at the distance of the moon, no rays of light can stray 

 except those which are scattered by our atmosphere as a 

 sun-illumined envelope. It is now very evident that the posi- 

 tion of the dark patch bordered by the line (b-c) and lying 

 partly over the western half of the moon, with respect to the 

 earth's shadow, is very anomalous. If the line (be) had been 

 curved concentrically to the centre of the shadow, it would have 

 been less surprising. The only way in which it can be accounted 

 for is by supposing the earth's atmosphere to have been very 

 opaque about the regions of the earth within the Arctic circle, 

 allowing very little light, if any, to be refracted, and, tracing 

 southwards that meridian along which the moon would be 

 setting at the time, the atmosphere getting clearer and clearer, 

 first in the upper strata and then in the lowest as we go south- 

 wards, until the equator is nearly reached. At 10.50 the moon 

 would be illuminated by solar rays refracted by the earth's atmo- 

 sphere and tangential to the earth's surface along the meridian 

 105° east of Greenwich (or thereabouts), which passes through 

 Irkutsk (in Siberia), Mongolia, Tonquin, and Siam, along which 

 line the inhabitants would see the moon going down inveiled in its 

 mysterious obscurity. It would be interesting to know whether any 

 observers noticed, at about the middle of the eclipse, any contrast 

 between the inner and darker shadow, in which the moon would 

 be largely immersed, and the outer regions of the shadow which 

 are illuminated dimly by both refracted and scattered light. The 

 unusual darkness of this eclipse, surprising, as it must have done, 

 all spectators, must be taken as a strong indication of great 

 opacity in our atmosphere. Another noticeable feature was the 

 unsymmetrical appearance of the illuminated crescent at 10.50, 

 when the northern cusp (/;) exhibited a bluish-white, shading oft 

 gradually from the brilliant white to the obscurity of the shadow, 

 while the other cusp seemed quite sharp and distinct. Observing 

 the eclipse both with the naked eye and through a 4^" equatorial, 

 neither my fellow observers nor myself noticed any other indica- 

 tion of a blue fringe than that appearing just at b, which seemed 

 to me therefore to be a real appearance, and not a subjective 

 effect of contrast, as there was not complementary copper colour 

 anywhere on the moon sufficiently strong to suggest the blue, 

 and if there had been I ought to have noticed the blue fringe 

 all along the edge of the shadow bordering on the crescent, but 

 it appeared to me of a neutral grey. 



Heworth Green, York H. Dennis Taylor 



The Red Light round the Sun — The Sun Blue or Green 

 at Setting 



I can confirm Mr. Backhouse's and Mr. E. D. Archibald's 

 impression about the colour now and for some time past seen 

 round the sun ; that it first appeared about November last and has 

 been more or less visible ever since. The colour was then, and 

 still is, sometimes rose, sometimes amber or buff. It is best 

 observed, when the sun on bright days is behind a cloud, round 

 that cloud, in the place where, at other times, broken beams of 

 shadow, thrown out from the cloud like a row of irregular 

 palings and deepening the blue of the sky, are to be seen. 

 Towards sunset it becomes glaring, and white and sallow in 

 hue. Something of a circular shape may then perhaps be made 

 out in it, but it does not seem to me that it ought to be called 

 a halo. A halo, as I understand, is a ring, or at least a round 

 space inclosed by a ring. This appearance has no ring round 

 it. Also in a halo (I have seen numbers) it is the ring that is 

 coloured — either throughout, or at four places where the ends of 

 the four arms of a cross would rest upon it ; and the inclosed 

 field is uncoloured or coloured like the rest of the sky : here 

 there is an uninclosed but singularly-coloured field. 



But whether we call the appearance a halo or not is perhaps 

 only a question of terms : to call it a corona, as Mr. Leslie 

 does, is another, and, as it seems to me, a hazardous thing, 

 because it would imply that what we are looking at is an ap- 

 pendage of the sun's own (and that too at a time when it is 

 strongly doubted if the sun has a corona of any sort of all), 

 instead of what is much easier to suppose, a terrestrial or atmo- 

 spheric effect. If there is going on, as Mr. Leslie thinks, an 

 " increase of sun power," this ought to be both felt and mea- 

 sured by exact instruments, not by the untrustworthy impressions 

 of the eye. Now Prof. Piazzi-Smyth says that sunlight, as 

 tested by the spectroscope, is weaker, not stronger, since the 



phenomena of last winter began. To set down variations in 

 light and heat to changes in the sun when they may be explained 

 by changes in our atmosphere, is like preferring the Ptolemaic 

 to the Copernican system. 



It is, however, right and important to distinguish phenomena 

 really new from old ones first observed under new circumstances 

 which make people unusually observant. A sun seen as green 

 or blue for hours together is a phenomenon only witnessed after 

 the late Krakatoa eruptions (barring some rare reports of like 

 appearances after like outbreaks, and under other exceptional 

 conditions) ; but a sun which turns green or blue just at setting 

 is, I believe, an old and, we may say, ordinary one, little 

 remarked till lately. I have a note of witnessing it, with other 

 persons of a company, in North Wales on June 23, 1877, the 

 sunset being very clear and bright. It is, possibly, an optical 

 effect only, due to a reaction (from the red or yellow sunset 

 light, to its complementary colour) taking place in the over- 

 strained eye at the moment when the light is suddenly cut off, 

 either by the sun's disappearance or by his entering a much 

 thicker belt of vapour, which, foreshortened as the vapour is 

 close to the horizon, may happen almost instantaneously. And 

 this is confirmed by a kindred phenomenon of sunset. If a very 

 clear, unclouded sun is then gazed at, it often appears not con- 

 vex, but hollow ; swimming — like looking down into a boiling pot 

 or a swinging pail, or into a bowl of quicksilver shaken ; and of 

 a lustrous but indistinct blue. The sky about it appears to swell 

 up all round into a lip or brim, and this brim is coloured pink. 

 The colour of the light will at that time be (though the eye 

 becomes deadened to it) between red and yellow. Now it may 

 be noticed that when a candle-flame is looked at through coloured 

 glass, though everything else behind the glass is strongly stained 

 with the colour, the flame is often nearly white : I suppose the 

 light direct from the sun's disk not only to master the red and 

 yellow of the vapour medium, but even, to the eye, to take on 

 something of the complementary blue. 



Even since writing the above I have witnessed, though 

 slightly, the phenomenon of a blue setting. The sunset was 

 bright this evening, the sun of a ruddy gold, which colour it 

 kept till nothing was left of it but a star-like spot ; then this 

 spot turned, for the twinkling of an eye, a leaden or watery 

 blue, and vanished. 



There followed a glow as bright almost as those of last year. 

 Between 6. 15 and 6.30 (Dublin time) it was intense: bronzy 

 near the earth ; above like peach, or of the blush colour on ripe 

 hazels. It drew away southwards. It would seem as if the 

 volcanic "wrack" had become a satellite to the earth, like 

 Saturn's rings, and was subject to phases, of which we are now 

 witnessing a vivid one. G. M. H. 



Dublin, October 19 



The Volcanic Dust (?) Phenomena 

 The changeableness of the wisps of this dust (?) is surprising. 

 On the 19th inst., near sunset, they were conspicuously visible 

 in all parts of the great corona round the sun, being definite in 

 form — narrow, and about 5° long ; it was the first time I had 

 seen them since (I believe) May 18, when they were only just 

 perceptible. During the intervening period the film or portion 

 of the atmosphere on which the universal sky phenomena have 

 appeared has been perfectly uniform in texture. On the 20th 

 inst. they were again conspicuous about sunset, extending faintly 

 even beyond the great corona ; they appeared horizontal in the 

 north-west. They were more or less visible about the same 

 time on the 23rd and 26th, on which latter date they could be 

 distinguished faintly in the semicircle opposite the sun at 7.30 

 a.m. and 4.8 p.m. 



It would be interesting to know how far the changes in then- 

 visibility are simultaneous over large districts : it appears that 

 they are not universal, for Mr. R. Leslie (Nature, October 16, 

 p. 5S3) describes them as distinct though very small in the early 

 part of July this year, at which period I never perceived a trace 

 of them in Switzerland. I take the "cloud forms " Mr. Leslie 

 describes to have been the same I am alluding to, though the 

 colour seems to have then been too faint to be perceptible at 

 Southampton. I cannot attempt to explain how the glare round 

 the sun was visible to him in 1882 or earlier, when the red part 

 of what seems to be the same phenomenon did not appear till 

 so long after. 



Observations on the motion of the wisps would be very useful 

 in showing the movements of the upper currents of the atmo- 

 sphere. I have made a few, but they are not very satisfactory. 



