APRIL 11, 1907] 
NATURE 
563 
the reviewer scarcely knows how to control his pen 
so as not to appear unduly laudatory. Yo say that 
the book is practically perfection is a mild way of 
putting it, for, as a matter of fact, it is one that 
can never be equalled or rivalled so long as the copy- 
right of its illustrations holds good, since no other 
man is likely to undertalke the labour and expense 
necessary to produce a similar series of pictures from 
nature, even if he had the energy and patience neces- 
sary to the task. How great a debt ornithologists 
and bird-lovers generally owe to the Messrs. Kearton 
(for a large number of the photographs have been 
taken by the author’s brother, Mr. Cherry Kearton) 
it is, indeed, impossible to estimate, and a part of 
their reward, at any rate, must consist in the 
pleasure they afford to, let us hope, an ever-widening 
circle of readers. 
Of the photographs of nests and eggs, as well as 
of those of the parent birds, it is impossible to speak 
too highly, and where all are on such a high level 
of excellence it would be almost invidious to select 
any for special commendation. The one here repro- 
duced has been chosen on account of its size rather 
than from any other consideration. The plates of 
eggs are admirable examples of the best style of 
three-colour process. Taken as a whole, the volume 
(which is a marvel of cheapness) will probably prove 
the most attractive natural history book of the 
year. 
THE ORIGIN OF “BOTTOM. WATERS” IN 
THE NORTHERN SEAS. 
SERIES of valuable tables and charts, in which 
the results of a great series of observations 
made in igo1 by Captain Roald Amundsen in the 
Arctic Seas are summarised, is contained in a mono- 
graph recently published.1 These observations are 
supplemented by, and compared with, results pub- 
lished by other observers, chiefly Russian and Nor- 
wegian, and as a collection of facts the little volume 
is certain to prove of great value to all students of 
oceanography. Dr. Nansen’s main purpose in the 
discussion of the observations has been the scientific 
explanation of the origin of the intensely cold and 
heavy ‘‘ bottom waters’’ found in the basins of the 
Norwegian seas and North Polar Ocean. In discuss- 
ing the scientific results of the Norwegian North 
Polar Expedition of 1893-6, Nansen had already dealt 
with this subject, and reached the provisional con- 
clusion ‘‘that the cold bottom water of the Barents 
Sea is divided into two portions; the northern cold 
water coming from the sea to the North, North East, 
and East; and the southern cold water having two 
or three sources, namely bottom currents from the 
East and North East, and the surface of the sea 
itself which is cooled during the winter.’’ In the 
light of more recent and extensive observations, 
Nansen has revised his opinion, and puts forward a 
different explanation of the origin of bottom water. 
This explanation accords with the facts observed, and 
may be briefly summarised. 
The conditions required for the formation of 
bottom water are that near the surface water shall 
be found having a salinity of about 34-9 per cent., 
and that during winter this water may be cooled 
down to —1°-3 C. or 1°-4 C. Its density may thus 
be between 28.11 and 28-13, and possibly greater, so 
that it becomes sufficiently heavy to sink. The 
1 *‘ Northern Waters : Capt. Roald Amundsen’s Oceanographic Observ~ 
ations in the Arctic Seas in 1901, with a Discussion of the Origin of the 
Bottom-waters of the Northern Seas.” By Fridthjof Nansen. Pp. 154; 
11 plates. (Christiania : Jacob Dybwad, 1926.) 
NO. 1954, VOL. 75] 
assumed salinity of surface water Nansen thinks will 
only exist in places where Atlantic water has mixed 
with Arctic water. Further, he considers that when 
bottom water is being formed there must be no rapid 
horizontal circulation which would bring in new 
supplies of relatively warm water. As the surface 
water becomes heavier it sinks, and will be replaced 
by somewhat warmer water of higher salinity, which 
in its turn will be cooled until it becomes heavier 
than the previous surface water, when it will sink 
still deeper, and be replaced by warmer water of 
still higher salinity from below. The uppermost 
strata will by this process be gradually increased in 
salinity, and approach that of the bottom water— 
about 34-9 per cent. The depth of vertical circulation 
will increase until it reaches down into the typical 
bottom water, and at that stage all strata from the 
surface downwards will have attained nearly uniform 
temperature, salinity, and density. Subsequent cool- 
ing at the surface will produce water so heavy that 
it may sink far down into the bottom water, or even 
to the bottom of the sea. 
The heaviest sea-water of which Nansen has any 
knowledge was found at a depth of 120 metres— 
8 metres above the bottom—off the coast of Nova 
Zembla in May, 1900; the temperature of bottom 
water has in some cases approached —2° C., with a 
salinity exceeding 35 per cent. and a density of 28.33. 
The observations made extended to depths of 3000 
metres, where the temperature was —1°%1 C. 
Amundsen reached 2000 metres, at which the tempera- 
ture was —1°-3 C. 
The circulation of bottom water in the Norwegian 
Sea Nansen describes as follows:—The bottom 
water is chiefly formed and sinks towards the bottom 
during the winter and spring in the regions between 
73° and 76° north latitude, and between 4° west 
longitude and 4° east longitude. From this region 
it moves along the bottom and spreads out laterally, 
producing cyclonic movements in the deep strata of 
the Norwegian Sea. During this circulation the 
bottom water is slowly heated from the underlying 
warmer sea bottom and from the overlying warmer 
water. In this manner its temperature near the 
bottom is gradually raised from about —1°-3 C. to 
about —1° C. Nansen estimates that at least two- 
thirds of the whole basin of the Norwegian Sea is 
filled with cold bottom water. The renewal of the 
cold bottom water in the basin of the Norwegian Sea 
must be an extremely slow process, and it has been 
established by actual observation that the bottom 
water does not extend across the ridge anywhere 
between Iceland and Norway, where the temperature 
is nowhere below zero. Further, he thinks that it 
is very improbable that any bottom water with a 
temperature below —1° C. ever gets across the ridge 
between Iceland and Greenland. 
For the North Polar basin Nansen considers the 
minimum temperature to be between —o°-8 C. and 
—o°.g C., the salinity being about 35-1 per cent. 
If existing observations are confirmed, in his judg- 
ment the possibility of a communication between the 
deep North Polar basin and the deep basin of the 
Norwegian Sea, as well as of their bottom waters, 
will be finally excluded. In that case he thinks that 
there are two regions where the bottom waters of the 
North Polar basin might originate by being cooled 
down directly through radiation from the sea surface, 
namely, in the seas north of Spitsbergen and near 
northern Nova Zembla. Nansen is further of opinion 
that the renewal of the cold bottom water of the 
enclosed North Polar basin will occur even more 
slowly than the corresponding renewal in the Nor- 
wegian Sea, so that a much smaller quantity of water 
