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climatology I should give, without hesitancy, 
the name of Dr. Julius Hann, the director of 
the Austrian meteorological service. 
In 1883 Dr. Hann published a long needed 
book, a general treatise on the climatology of 
the whole earth’s surface. This work was the 
outcome of many years of special study and 
research, and required several years of direct 
labor in its actual writing. It was received 
with enthusiasm by the German reading scien- 
tific public, and English readers deplored the 
fact that we had no corresponding work in 
English. Fourteen years haye now elapsed 
since Hann’s work first appeared, and its 
second and greatly enlarged and rewritten edi- 
tion finds our language still without any gen- 
eral work on climatology. We have not even 
a translation to fill the place which should be 
occupied by a work of honest English or Amer- 
ican authorship, and it is to be hoped that some 
publisher will be induced to take advantage of 
the appearance of this new German work by 
bringing out a translation of it either in full or 
in abridgment. 
Hann’s climatology consists of three vol- 
umes. The first is devoted to general climato- 
logical conditions, in which the relations of 
cause and effect are discussed for the various 
meteorological elements. The second yolume 
is devoted to the special climatology of the 
regions embraced in the tropical zone. The 
third volume treats of the climate of the tem- 
perate and cold zones. 
One serious drawback to the usefulness of 
the work is the lack of climatological charts; 
but the author explains that they were omitted 
because they would considerably increase the 
price that must be asked of purchasers of the 
present treatise, and, moreover, such charts 
had been published elsewhere in easily access- 
ible form. 
The 404 pages of Vol. I. contain: A general 
idea of the scope of climatology ; and complete 
explanations of the nature, importance and re- 
lation to each other of the climatic factors, 
temperature, humidity, precipitation, cloudi- 
ness, wind, air pressure and evaporation. A 
short statement of the composition of the air 
and the impurities which it may contain, to- 
gether with some remarks on plant phenology 
SCIENCE. 
(N.S. Von. VI. No. 157. 
as related to, and dependent on, climatic con- 
ditions. A brief though comprehensive review 
of our knowledge of the amount of radiation 
from the sun and the resulting ‘solar climate.’ 
The principal forms of telluric or physical 
climate, which is the solar climate modified by 
the earth’s atmosphere and the existing distri- 
bution of land and water; this naturally occu- 
pies the greater portion of Vol. I. And, finally, 
the meteorological cycles and climatic oscilla- 
tions. 
Let us notice more particularly some of the 
most interesting facts given by the author. 
Owing to the elliptic form of the earth’s orbit, 
by which the earth is sometimes a little nearer 
the sun than at other times, the southern hemi- 
sphere receives more solar heat in summer and 
less in winter than the northern hemisphere. 
If our earth had no atmosphere the average 
temperature at the earth’s surface would be, at 
the equator for the hottest month 67°C. and for 
the coldest month 56°C., and at the poles for the 
hottest month 82°C. and for the coldest month 
—2738C. (which latter is, curiously enough, the 
absolute zero of the thermometric scale). 
Concerning the interesting question of the 
effects of forests on rainfall Hann says that 
from the nature of the case it is almost impossi- 
ble to prove anything by direct measurements, 
and that the increase of rainfall due to forest 
growth has been far over-estimated. It is quite 
probable, however, that in the tropics the 
woods do slightly increase the amount of pre- 
cipitation, and extensive woods in the middle 
and higher latitudes probably increase the fre- 
quency of rainfall. 
The effects of mountains on rainfall has re- 
ceived thorough treatment at the hands of the 
author, and especially that peculiar phase of 
increase of rainfall with the altitude up to a cer- 
tain level, and the subsequent gradual decrease 
at greater heights. With an increase of alti- 
tude amounting to from 2,000 to 4,000 feet the 
rainfall may be increased by from 50 to 250 per 
cent. This increase of rainfall is due to the 
condensation of the moisture in ascending air 
currents which form on mountain sides. 
It has been computed, retrospectively, that 
in Jurassic times the mean temperature of the 
earth was about 2°C. warmer than it is at pres- 
