36 
NATURE 
[MarcH II, 1915 


Magazine appears correspondence on this subject by 
Dr. Rambaut, myself, and others, and the editor, 
Dr. Mill, in summing up the matter, decided strongly 
in favour of the dispersion theory. Capt. Carpenter, 
R.N., whose numerous observations appear in the 
British Astron, Assoc. Journal, holds the same view. 
It is quite true that, if I look steadily at a bright 
red sun, and then close my eyes, I see a green after- 
image, but this is just what the observer of the 
green flash should not do. He should avoid looking 
at the sun when it is bright, and should wait until it 
is so low that the eye can easily bear the light— 
should wait, in fact, until only a very small segment 
visible. As before stated, with a really red sun 
the flash fails to appear, so far as my experience 
goes. If proper precautions are taken I do not think 
any appreciable after-image will be present. 
I may point out that the nature of the horizon, 
provided it is clean-cut and low down, makes but 
little difference. It may be of cloud, land, or water, 
and, of course, the last the best. My experience 
relates to all three. 
But few persons appear to have used a telescope 
for observing the flash. If those who have not done 
so would observe a low.sun with a power of, say, 
too, I think that they would be. convinced that the 
true cause was atmospheric dispersion. 
The real mystery about the flash is that it so often 
fails to: appear, when apparently all conditions seem 
favourable.. I have not yet found any explanation of 
this, but I am inclined to the opinion that at a clear 
sunset the flash could always be seen if a telescope 
were available, though it might be too feeble for the 
naked eye, for a telescope invariably reveals the upper 
green fringe when the sun is low. The telescope, of 
course, was achromatic, and showed no colour with a 
high sun. To the Journal of the B.A.A., to that of 
the Leeds Astron. Society, and to the English 
Mechanic I have contributed very numerous notes on 
this subject; but references to them would occupy too 
much of your valuable space. C.D Waiter, 
Invermay, Hyde Park, Leeds, February 22. 
is 
is 
The Prices of Chemicals. 
IT ave had the same experience as ‘‘S. P.” Since 
my letter of February 18 I have been able to purchase 
dulcite at 60s. an ounce from a firm of dealers in 
chemicals other than the one to which [I referred. I 
cannot admit, therefore, that my complaint was un- 
justifiable. 
University of Liverpool, March 2. 
THROUGH SIBERIA. 
HIS book is the diary of a very interesting 
journey accomplished by the author in the 
course of the autumn of 1913. In fact, it 
describes four different journeys: one from 
Tromsé, via the Kara Sea, to the mouth of the 
Yenisei; then up the Yenisei to Krasnoyarsk; 
next by rail across Transbaikalia and Manchuria 
to Vladivostok on the Pacific; and from this port 
to Petrograd, by the Usuri and the new Amur 
railway and the main Trans-Siberian line. A 
remarkable feature of this journey, during which 
more than 16,000 miles were covered, is that it 
was accomplished in less than three months, from 
August 5, when the party started from Tromsé, 
1 “*Through Siberia, the Land of the Future.” 
Translated by A. G. Chater. Pp. xvi+478. 
1914.) Price 15s, net. 
NO. 2367, VOL. 95] 

By Dr. F. Nansen. 
(London: W. Heinemann 


to October when Dr. Nansen reached 
Petrograd. 
We cannot expect to find detailed descriptions 
of the different portions of the immense continent 
thus rapidly crossed; but the book throughout 
has the greatest interest,-owing to the human 
element it contains, and the unexpected glimpses 
it gives of the Canada of the East, with its 
wonderful development during the last fifteen 
years. In addition, it is lustrated by more than 
160 beautiful photographs, taken by the author 
himself, most of which are worth pages of 
descriptions. The ethnographical remarks about 
the northern natives, whose encampments, or 
boats, Dr. Nansen always found time to visit, 
especially about the remaining members of that 
curious, once numerous, nation, the Yenisei 
Ostyadks, will be read with a special interest; 
while the photographs, as may be seen from the 
two accompanying specimens, give a clear idea 
of the ethnographical types of the different native 
tribes. 
The really difficult part of the journey, from 
Troms6 to the mouth of the Yenisei, was made on 
the steamer Correct, with the experienced pilot 
Capt. Johannsen, without meeting with serious 
difficulties. There was a good deal of ice in the 
Kara Strait, and especially further east, so that. 
the Correct had to enter the Kara Bay in order 
to follow the narrow, more or less ice-free channel 
close to the coast of the Yalmal peninsula. There 
was only one dangerous accident, when the 
steamer stuck on a mud bank close by the Devil’s 
Island; but otherwise the journey was quite 
successful, and it took only eighteen days from 
the day the steamer entered the Kara Strait to 
the day it reached the port at Nosonovskiye 
Islands, in the Yenisei, under the 71st degree of 
latitude. 
Once more the practicability of the northern 
route to Siberia was thus demonstrated. But it 
must be said that the conditions of ice along the 
northern coast of Siberia show great variations 
in different years, and in-1913 they certainly were 
by far not so favourable as they were in the 
years 1870-1871 and 1875-1878. A very valuable 
appendix, where the average summer tempera- 
tures on the shores of the Kara Sea and the con- 
ditions of ice in that sea are given for the last 
forty-one years, shows that while this passage 
was remarkably free from ice in the years named, 
as well as in 1890, 1897, 1990, 1g01, and 1904, 
the conditions were not favourable for navigation 
in 1883, 1884, 1888, 1911, and 1913, unfavour- 
able in 1895 and 1902, and most unfavourable in 
1903 and i9r2. 
Still, Dr. Nansen is certain that the northern 
route may become a regular line of traffic if cer- 
tain measures are taken. During his journey up 
the Yenisei, and later on along the Trans- 
Siberian railway, he had full opportunities to 
discuss such measures with M. Viestrétin, a 
Russian merchant and member of the Duma who 
has great knowledge of the Siberian north, and 
also made the journey on the Correct, and 
27) 
