118 
would be discovered, and a safe return would be ensured ; 
for the advanced parties would be able to fall back upon 
their consort, whence, in case of accident, the whole 
expedition could retreat to the Danish settlements in 
Greenland. 
The direct advantages offered by this route are, the 
discovery of the northern side of Greenland, and the 
prospects of securing the most valuable results in the 
various branches of scientific research,—in geography, 
hydrography, botany, zoology, ethnology, geology, geo- 
desy, and meteorology : but all the advantages to science 
cannot possibly be foreseen. Among the possible results 
enumerated by the Geographical Society are these :— 
Completing the circle of Greenland, ascertaining the extent 
and nature of its northern point, and discovering the 
conditions of land and sea in that area; supplementing 
the investigations of the Challenger expedition as to the 
bottom of the ocean ; the probability of forest vegetation, 
proved to have flourished on what is now the Greenland 
coast, having extended over the Pole itself, thus confound- 
ing all previous geological reasoning as to the climate and 
conditions of the globe during the Tertiary period ; a more 
complete knowledge of the teeming life of the Arctic 
Ocean ; a knowledge of the customs and mode of life of 
the supposed dwellers in the unknown area, of whose 
former existence there is proof, who have no communi- 
cation with the most northern known people, and who 
have probably been isolated for centuries ; a knowledge 
of the kinds of microscopic vegetation inhabiting the 
northern Greenland seas, which would throw great light 
on investigation into the age of the rocks of our own 
island, and on the later changes of the climate of the 
northern hemisphere, besides the geological results, in 
rocks and fossils, and the observations on glacial action, 
which would be yielded by the examination of a long 
coast line ; observations of the pendulum and of the dip 
and intensity of the needle ; and observations as to tem- 
perature, pressure, winds, a currents. These manifold 
advantages, of the highest importance—in spite of the 
vague Philistine tirade of the Z7%es—are confirmed 
and supplemented by the documents of the other 
societies. 
As to the element of danger, it is clearly shown in the 
Linnean Society’s paper that, as compared with explo- 
rations in Africa, Australia, and elsewhere, Polar voyages, 
North and South, show a comparative immunity from loss 
and hardship; and during the last few years experience 
has been so fruitful in her teachings, that the element of 
discomfort and danger may now be reducedto aminimum. 
The Geographical Society concludes its documents by 
adding to the other advantages that another generation of 
naval officers will be trained in ice navigation,—-and they 
will be needed in 1882,—that opportunities will be offered 
for distinction, and that a great benefit will be conferred 
on the Navy, and through the Navy on the country. The 
belief is expressed that all classes of the people will unite 
with men of science in the desire that the tradition of 
Arctic discovery should be preserved and handed down to 
posterity, and that Englishmen should not abandon that 
career of noble adventure which has done so much to 
form the national character, and to give our country the 
rank she still maintains. 
All this is irresistible. 
NATURE 
[Dec. 19, 1872 
FORESTRY IN ITS ECONOMICAL BEARINGS 
O what extent the climate of any portion of the sur- 
face of the earth can be changed by human labour 
is still an open question. Certain districts of the globe we 
are accustomed to look upon as condemned by Nature to 
perpetual sterility. The arid deserts of Africa and Central 
Asia, the frozen realms of Siberia, appear as if predestined 
to a gloomy lifeless solitude. To reclaim them to human 
control and human habitation may be one of the problems 
of the future. That climates have changed materially 
within recent times, we know as a historic fact. Macau- 
lay has made us familiar with the damp fogs and per- 
petual rain-clonds with which our island was invested 
during the period preceding the arrival of the Danes and 
the Saxons. Much of the amelioration of climate which 
has since taken place is doubtless due to the increased 
cultivation of the land, and the extent to which the fen- 
districts have been drained ; but the main agent has pro- 
bably been the destruction of the forests which then 
clothed a large portion of the island. 
The mode in which forests act in increasing the amount 
of moisture in the atmosphere is much misunderstood. 
Even in an article which recently appeared in the pages 
of so well-informed a journal as the Pa// Mall Gazette, 
it is affirmed that this effect is due to the attraction exer- 
cised by the trees on the rain-clouds. The principle by — 
which trees act in effecting this is, however, at least 
mainly, by acting as pumps in drawing up the superfluous 
moisture from the soil. The most trustworthy experi- 
ments show that, under normal circumstances, plants « — 
have no power of absorbing through their leaves water, 
either in the fluid or gaseous state; their supplies are 
obtained entirely through their roots ; and the superfluous _ 
moisture is evaporated from the leaves. The amount of 
aqueous vapour thus delivered into the atmosphere by 
vegetation is enormous, and has been the subject of care- 
ful investigations by French and German botanists. Von 
Pettenkofer recently detailed* some experiments on the — 
amount of evaporation from an oak tree, made during the - 
whole period of its summer growth. He found the amount 
gradually to increase from May to July, and then decrease 
till October. The number of leaves on the tree he esti- 
mates at 751,592, and the total amount of evaporation — 
in the year at 539'16 centimetres of water. The average — 
depth of rainfall for the same period on the area 
covered by the oak tree would be only 65 centimetres ; 
the amount of evaporation is thus 8} times more than that 
of the rainfall. The excess must be drawn up by the © 
roots from a great depth; and thus trees prevent the — 
gradual drying of a climate, by restoring to the air the 
moisture which would otherwise be carried to the sea by | 
streams and rivers. ; 
The immediate result, therefore, of the diminution of 
forests in a thickly-woodel country will be to increase 
the proportion of the annual rainfall that is carried to the © 
sea by the natural drainage of the country, and propor- 
tionately to decrease the amount returned insensibly to 
the atmosphere, which then condenses into rain and ; 
cloud. Within certain limits it is obvious that this” 
must be an unmixed good ; but as the country becomes | 
more and more thickly populated, and the land more 
+ Sitzungsberichte der k. bayerischen Akademie der Wissenschaften zt 
Miinchen, 1870, Band 1, Heft x. 
ans 
