342 
NATURE 
[ FEBRUARY 7, 1907 
in my letter written on January 6 (NaTuRE, January 24, 
p- 294). On his results, a normal river supply of the 
supposed uranium would in 90,000 years suffice to give the 
ocean its present radio-activity. In short, practically the 
whole of the uranium has to be accounted for in the sedi- 
ments. Mr. Eve perceived the difficulty, and suggests that 
the sediments are, indeed, its destination. I have already 
referred to the difficulties attending this view. 
Prof. Sollas’s contention (p. 319) as to the probable 
original character of the uranium in zircon is, I think, 
unanswerable. I had this fully in view when referring 
to uranium-bearing minerals in certain rocks. In certain 
rock masses the zircon might be the chief or entire source 
of radium, but it would appear that this cannot possibly 
be the case with ordinary granites. The analysis made 
by Mr. Strutt of a Cornish granite showed that less than 
one-ninth only could in this case be so accounted for. 
Mr. Strutt directs attention to this. Again, Prof. Sollas 
shows by the analysis he cites that this granite was prob- 
ably unusually rich in zircon. In Mr. Clarke’s last re- 
port of analytical work done in the laboratory of the 
United States Geological Survey (Bulletin No. 228) I have 
found nine granites-in which the zirconia is determined. 
The highest percentage was 0-08, and the others ranged 
from 0-04 downwards to a trace. Mr. Clarke in Bulletin 
No. 148, speaking of zircon, says of igneous rocks 
generally :—“* It may rarely be present up to a few tenths 
of 1 per cent. of the rock.’’ He also gives, as roughly 
approximate, that the average content of zirconia in 
igneous rocks is 0:03. This would imply a quantity of 
zircon adequate to account for barely 4 per cent. of the 
mean radium content of igneous rocks. 
There are, probably, other radio-active minerals possess- 
ing an original store of uranium, but I think Mr. Strutt 
has shown good reason for believing that the chief radium 
carrier is the mica, at least in granites. This is a mineral 
which from its properties would be very likely to absorb 
and retain.substances in solution. k vjejor: 
Trinity College, Dublin. 
The Green Tints of Sunset. 
THE appearance of a green light at sunset, like many 
other phenomena supposed to have only recently attracted 
attention, was noticed and commented upon by the ancient 
Egyptians, and more particularly so because in the clear 
air of Egypt the tints of sunset are peculiarly distinct. 
As the sun there descends nearer and nearer to the 
horizon, apparently-hastening to disappear behind one of 
the Libyan hills, as if burying itself in the sand at their 
base, the immensely enlarged flaming disc suddenly be- 
comes, for an instant, of a brilliant green colour, and 
immediately a series of green rays suffuses the sky in many 
directions, well-nigh to the zenith. ; 
The same phenomenon appears sometimes at sunrise, but 
to a smaller extent. 
According to ancient Egyptian notions of cosmogony, the 
sun, aiter passing through the western gate into the 
world of night, travelled northward parallel to the Nile 
until’the sixth hour, when it commenced to journey south- 
ward, having passed to the eastern side of Egypt, and, 
finally, at sunrise came forth by the ‘‘ Gate of the East.” 
Now, during the nocturnal voyage, the solar orb was 
said to be a disc of Mafkait, which was the title of a 
green-coloured mineral, and so the sun was considered 
from sunset to sunrise to be coloured green. Sometimes, 
just as the last part of the sun’s disc vanishes, its colour 
changes from green to blue, and so also after it has dis- 
appeared the sky near the horizon is often green, whilst 
toward the zenith it is blue. This was alluded to in 
ancient Egyptian writings, where sometimes it is said that 
at sunrise or sunset the sun’s rays were of Tahen, a blue 
metal, the title of which is often used in reference to the 
blue of the sky. 
_In Egyptian thought day was the emblem of life and 
night that of death, and the nocturnal sun being identified 
with Osiris thus rendered Osiris the god of the dead. The 
setting sun being green, therefore Osiris, as the nocturnal 
deity of the dead, was on the monuments and represent- 
NO. 1945, VOL. 75] 
ations of him when referred to as god of the dead painted 
green, as were other funerary divinities, such as Sekar, 
the form of the dead Ptah, which was that of a mummy 
with face and hands coloured green or dark blue. The 
splendid coffins of the high priests of Ammon, all the 
decorative tableaus of which are painted, frequently depict 
the green sun, and deities such as Anubis, god of the 
funerary journey, Isis, Nephtys, and Osiris are coloured 
green. 
It may be interesting, if possible, to decide whether the 
Egyptians recorded their observation of the green colour 
at Sunset in very early times. The late M. Groff, who has 
treated upon this point in the Bulletin de l'Institut 
Egyptien, proved that they did so as early as the fifth 
dynasty, by showing that a monument of that date de- 
lineates the half disc of the setting sun by a figure painted 
in three successive bands, the two lower, that is to say, 
those abutting on the horizon—of green, and the upper 
one of blue. 
This is not the proper place to discuss the innumerable 
instances upon Egyptian relics of representations relative 
io death being coloured green. It is undoubtedly the case 
that the practice arose from the green tints of sunset and 
sunrise, but it may justifiably be said that in the green- 
coloured sun disc referred to, which dates 5000 years back, 
we have the, at present, earliest known human record of 
un astronomical phenomenon. JosEepH OFFORD. 
2 Fairfax Road, Bedford Park, W., January 29. 
February and March Meteors. 
Fesruary and March meteoric showers have never been 
sufficiently investigated. No very special displays have 
invited abundant observation, and, moreover, cold and 
cloudy weather often prevails at this season. Meteors, 
too, are generally rare, and from these several causes few 
observers have made persevering efforts to determine the 
strengths and positions of the radiants visible. 
In 1877 and 1887, February—March, the writer at Bristol 
obtained some observations, but they were altogether in- 
sufficient to reveal more than a small minority of the 
meteoric streams of this period. Giuseppe Zezioli at 
Bergamo, and Lieut.-Colonel G. L. Tupman in_ the 
Mediterranean in 1867-71, effected many valuable observ- 
ations in Febraury and March, and perhaps their results 
are the best secured up to the present time. 
With the earth approaching aphelion, meteors are 
usually scarce, though there are a number of interesting 
showers visible, and fire-balls are invitingly plentiful. But 
the firmament not having been thoroughly watched during 
the latter part of the winter season, an earnest, perse- 
vering, and accurate observer has a very promising field 
before him, and may expect to discover more new showers 
than are likely to reward his vigils under summer and 
autumnal skies. 
A number of streams presented during February and 
March have been already detected, but there is a large 
majority of very feeble systems still awaiting recognition. 
The visible strengths of many showers vary from year to 
year, and there are periodical displays which only occur 
at long intervals, so that fresh observations are very 
desirable if our knowledge is to keep pace with the develop- 
ments frequently occurring. 
Fireballs are often numerous on about February 1o and 
March 1-4. Some of the radiant points of ordinary 
shooting-stars recorded at Bristol are :— 
February March 
75+41 7-23rd 161+58 end 
134+67 and in March 166+4 beginning 
147+6 177+48 end 
158+ 28 190+58 middle 
175+10 196+ 44 
181+34 20th 229+32 end 
204-10 13-2Ist 254+55 14th 
236+11I 13-20th 263+62 end 
263+36 20th 270+47 middle 
332471 316+ 76 
Bristol, February 4. W. F. DENNING. 
