, 1922-10-12
Green Flash at Sunset

when the sun sets behind a dis
tnnt and clear horizon It's last ray
disappear with an emerald green
fash" notes Mature. The coioration
Is due to the ~refrzct.on Of light in our
atmosphere by which the suns image
Ia raised through about half a degree.
the elevation Increasing from the red
10 the violet end OF the spectrum. A.
the violet and 20 some extent the blue
rays are absorbed By the layer OF air
through which tho Hight has 10 PASS
IL Is the blush green part OF the spec
trun that is dominant al the ultimate
moment of unset.
This seems clear enough and even
obvious. But there are always CERTAIN
.uinds that di-frust the obvious. not
always TO the disadvantage % science.
and others which rebel against a com
monpiace explanation o. a striking et-
fect. Imagination Is always ready TO
supply more or less fancifui ~slfe-aS-
tives leading to controversies AMI cor
rsspondence In scientific journals
I'm this \ a considerable
amount OF literature on the green
flash has accumulated. and this is noT
J collected by Professor 81. L. Muider
I n a volume OF 40 pages. The two
serious alternative explanations that
have been offered TO replace h \
based on the dispersion OF light IN our
| atmosphere might b dismissed in :
sentence. The green fash snnot he
the after image In an y fatigued by
the red light o, the u because Il
appears At slnris- as wci = : At sun
| sot: nor en- 4 derive lte fsoior from sc-
;ual passage through the sea, because
I IL also seen when ,ie "a disap
|, GEARS behind a land horizon.
I'VE note with interest that the first
,rii ted description OF the green flash
hat car be traced is contained in a
| novel by Jules Verne entitled lie
RAyon Vert and published in 1889.
Perhaps some readers OF Nature can
verify the lett motif OF TIRE stn--. tSker
apparently from a Scotch legend. &C
sording to which those wno have once
seen the green ray acquire the power
Of seeing what is IN the hearts OF
others as well as in the.r own.
1T the authors investigation OF the
scientific literature lie a. exhaustive
rs II appears TO he the first scientific
roties OF the green fash was pub
'ished only in 1885. IN Chevreuil
communicated to the French Academy
observations made in the Indian ocean
by Trsves. who adopted the erroneous
'heory OF Complementary eoior.. Ae-
-ording to Professor Muider's own
Wow a complete explanation is still
wanting. although he agrees that It
must he based on the dispersion the
Dry. But I would suggest that his res
srvsticns depend almost entirely on
he importance he attaches 10 dlscrep
tnoies in the descriptions - different
Observers and in their Estimates of
the duration of the flash.
apart from real differences in at.
nospheric conditions that may be very
considerable It IL not to be expected
hat men not specially trained in such
'baervations could tel with any de-
gree Of certainty whether an outburst
II light lasts a tenth OF a second or
'wo seconds. Some have described the
lash as appearing in the form OF a
hort line, while on Others Il has left
10 impresZon OF shape. The author.
who has been a professor Of ophthal-
mology. is not likely to have forgotten
the possible effects Of a~stiematism.
but ever q perfect eye might see 2