LETTERS TO THE EDITOR. 
(Zhe Editor does not hold himself responsible for opinions ex- 
pressed by his correspondents. Neither can he undertake 
to return, or to correspond with the writers of, rejected 
manuscripts intended for this or any other part of NATURE. 
No notice ts taken of anonymous communications.) 
Heights of Sunset After-glows in June, 1902 
THERE was a very fine example of red sunset after-glow 
visible here on the evening of the 26th ult., which presented 
with rather remarkable appropriateness to the date of its ap- 
pearance, as immediately occurred to me while watching the 
impressive sight, a scene of transcending splendour of nature’s 
own elaboration which could hardly have been much surpassed 
in grandeur by what England’s great display of rare illuminations 
on that night would undoubtedly have been, if a check most 
sorely sad and grievous had not interposed a throb of deep 
sorrow on the nation, eliciting good proofs of its heartfelt 
sympathy and loyalty so universally and strongly as to prevent 
those sumptuous light displays from being used as auspiciously 
as they were hoped to be to celebrate the joyfully expected 
**Coronation-day ” of 1902. The sun set at about 8h. 25m. 
with its orange-yellow disc unhazed, and only shorn of rays by a 
few faint cirrus cloud-streaks close to the horizon, the sky being 
elsewhere apparently quite free from clouds. At about 8h. 4om. 
a long low belt of sky extending 70° or 80° along the north- 
west horizon had grown orange-yellow, streaked with a few 
faint lines of red and gradually diluted upwards at a height of 
15° or 20° into pale shades of light yellow. A ruddiness of the 
sky in the east had at the same time risen nearly to the zenith, 
and through its natural blue tint there the sky passed gradually 
to white about half-way from the zenith to the west horizon, 
while under this white tract (about 30° in width) lay the 
bright belt of orange light with its shades of yellow gradually 
deepening downwards. But at about 8h. 45-50m. the pure 
white interval between the ordinary blue and the yellow-tinted 
regions was gradually invaded, and at last quite occupied, by 
the advancing ruddy colour from the east; and until about 
8h. 55m. a space from 30° of altitude in north-west to near and 
somewhat beyond the zenith, and for 40° or 50° to either side 
of a vertical line through the place of sunset, presented a broad 
expanse of rich rose-coloured, lake-red light pervading all the 
sky’s north-western quarter with a fine wide blaze, against 
the purple glare of which tall trees and houses all looked sharply 
silhouetted, and for a short space of about ten minutes that the 
rose-red colour lasted, all objects of the landscape facing to- 
wards the west looked conspicuously crimsoned. The ruby- 
tinted glow sank rather rapidly in height, and by 9 p.m. it had 
subsided into the summit of a lower and far brighter pinkish- 
orange bank of light about 30° high, the lower layers of which 
formed a belt 12° or 15° in height stretching for about go” along 
the west-to-north horizon in a blaze of yellow amber or of ochre- 
yellowcolour. No radiating streamers or shadow-beams crossed 
either the previous purple glow or this orange-reddish. dome- 
like bank of light ; but the latter light-field’s splendid flood of 
unflecked, evenly-spread colour sank very gradually, preserving 
its length, to 12° or 15° in altitude by 9h. 15m., growing less 
ruddy, and assuming pretty uniformly then throughout the 
horizon layer’s yellow-ochre colour. As its brightness had then 
very sensibly diminished, no further watch was kept on its 
later changes of appearance. 
The time of occurrence of the true rose-tinted glow, when the 
white space’s illumination was replaced, and then swept down 
into the sunset-glow, by a westward coursing wave apparently, 
of rose-tinted light, was about Sh. 50-55m. when at its 
brightest, or about 25-30m. after sunset, when the sun was 
therefore about 3° below the horizon here, and when the earth’s 
shadow-surface cast by the sun through the air above this point 
of view was about five miles from the earth’s surface. The finely 
divided matter which by a red-bordered coronal or ‘‘ Bishop’s 
ring” effect! of diffraction, probably, on an exceedingly wide- 
1 The ring was thus described by Mr. S. E. Bishop, at Honolulu, in 
Nature (vol. xxix. p. 260, 1884, January 17):—As ‘‘a very peculiar 
corona or halo extending from 20° to 30° from the sun, which has been 
visible every day with us, and all day, of whitish haze with fAzukisk tint 
shading off into /f/ac or purple against the blue. . . It is hardly a con- 
spicuous object."’ In the growing dusk, however, of an hour after sunset. 
the ring of pinkish white and purple, probably produced by admixture of 
the sky's ordinary blue with the yellow, orange and red parts of a pure 
corona, however weakly visible in full daylight, might yet in twilight look 
bright enough to be easily distinguishable; and the gradual shrinking 
wo. 1708, VoL. 66] 
NATURE 
[JuLy 24, 1902 
circle scale, bent downwards into view from nearly overhead 
the sun’s parting rays in the westward coursing way which 
seems to be quite general in these dust-caused colour-glows, 
and with red colour made rosy, probably, by mixture with the 
sky’s ordinary blue, must thus, it appears, have been at no very 
considerably greater height in the atmosphere than about five 
miles ; or at about the ordinary floating level of cirrocumulus 
and cirrostratus clouds. 
A few less radiant after-glows of rosy tinge appeared here 
when the sky was clear, on June 17 and 21 ; but no perceptible 
traces of rose colour occurred in the pallid sunsets of June 23 
and 25, although the sun went down on the latter date behind a 
faint low bank of cirrus cloud, surrounded by a splendid orange- 
yellow ‘‘glory”” about 10° wide, very suggestive of ‘‘ Bishop’s 
ring,”’ as it was shaded off by redder colour at its borders. As 
the last visible spark of the sun’s bright orange body disappeared 
in a little cleft, apparently (for it lingered there for a second or 
two), of a tree-clad hill horizon four or five miles distant, it was 
white (and the same was noted on the: 26th), and showed no 
greenish coloration.'_ Under the north-western edge of a thick 
cloud-veil which overspread the sky on Sunday evening, June 22, 
a belt of sky about 40° long and about 10~15° high was. 
brilliantly ablaze, from gh. to gh. 15m., with light of orange- 
yellow colour slightly streaked with red, and presented, among 
fragments of dark cloud dispersed across it, an almost terrifying 
resemblance to reflection in the sky of an immense distant con- 
flagration. On June 24 a ruddy yellow glare widely pervaded 
the clear sky to a high altitude in N.W. from 8h. to 8h. 30m., 
but I was not fortunate enough among obstructions of its view 
in London to obtain any observations of its changes. On two 
other evenings, however, Friday and Saturday, June 27 and 
28, sufficiently clear views of the rose-tint were seen, the 
times of apparition of which were recorded, to afford ad- 
ditional determinations of the real height of its appearance ; 
and the following are some details of the pink glow’s aspect on 
the three or four dates besides June 26 when its successive 
changes here were pretty clearly recognised and were ap- 
proximately noted. 
On June 17, the first clear evening after a cold, rainy fortnight,. 
a pale cochineal tint, in the north-west, of the beautifully trans- 
parent sky was first quite plainly noticed, at 9h. 10-15m., of some 
width and at an altitude of about 10°30" ; although a similar, 
but rather weaker, pink glow had already before been seen with 
rather less distinctness on the last two nights of May; and on 
this evening it faded out by 9h. 15m., sinking down intoa brick- 
red light-glare 510° high, which by about gh. 20-25m. grew 
dull orange-yellow and then faded. The first commencement 
of the glow was not seen, but as it was probably near its 
inwards of this distinct red bordered ring from nearly overhead towards the 
west as the remaining upper levels of the atmosphere still lighted by the sun's 
rays grow every moment loftier, must pretty surely indicate that the first 
red light to fade away, or that beginning nearly overhead and furthest from 
the sun, belongs at once to both the lowest and the finest-grained dust- 
layers of the corona-forming haze ; a conclusion nowise inconsistent with a 
usually experienced property of mists that they most commonly become 
coarser-grained in retreating inwards from their borders. 
1 Theearliest mention that I have seen of the ‘‘green-flash” at sunset, 
as having been sometimes observed on the sea horizon from Bude, in Corn- 
wall, by the Rey. G. H. Hopkins (NaTuRE, vol. xxix. p. 7, 1883, Novem- 
ber 1), concludes witha remark that the effect was not produced when the 
sunset behind a distant cloud, and that it might very probably be also seen 
at sunrise. ‘This last conjecture was immediately confirmed (¢éid., p. 76) 
by Prof, W. Swan, who wrote from Edinburgh that when watching for 
sunrise on the Rigi, on the very clear morning of September 13, 1865, he saw 
the sun appear with a dazzling blaze, for the first instant, of superb emerald 
green colour, from behind the sharp outline of a distant mountain. It may 
be interesting to add here, with respect to the other condition noticed by 
Mr. Hopkins, of the green flash not being apparently produced by the 
sun's descent behind a cloud, that having been myself, with three others 
(two of us using binocular field-glasses), well placed on April 22 last for 
trying to observe the totally eclipsed moon in the east and the setting sun 
in the west above the horizon together, the sun at least, after a cloudy and 
rather stormy day, set in an opening of clear sky, behind a low bank about 
2° or 3° high, of sharply edged, opaque and solid-looking cumulus which, 
judging from the ten miles distant ridge of hills at Cookham, very far behind 
which the cloud-bank seemed to lie, could hardly have been less than 20 or 30 
miles from our position. Passing the word to ‘‘ look out for colour,” when 
the sun’s upper limb was nearly disappearing, we all exclaimed ‘‘ green!” 
together, as the last and most northerly light-speck of three bright beads. 
into which the sun's upper limb broke up atlast lingered for not much more 
than half a second after the other two, both of which looked rather whiter 
than the last, when fading, and then vanished. Of the last spark’s distinctly 
green colour there could be no doubt, and it inclined rather to a yellowish 
than toa blue shade of green. A thin thread of yellow light, like an ex- 
tremely slender, short, crooked horizontal lightning flash, fringed the dark 
cloud’s upper edge for afew minutes, behind which, at about 7h. 15m., the 
sun had descended ; and beyond that the clear sky was nearly grey, and 
until about 7h. 3om., like the sun's disc itself, very free from yellow and 
orange sunset colours. : 
