, 1877-06-06

sage over co u s%nltdceS, ar condensed lutO
clouds and fall in rain. in pres, nee Of
S.W. or other SEA wind the amount of
rainfall will depend yely much upon the
temperature of the soil a hot, a i'll sill
heallLg the air above it. and thereby eua-
bling that air 10 retain il the form Of invi-
slble moisture the largest r0Ssib G duaEti-
ty OF water; white when vapOul-Iaden
winds pass over Il cola surface they are
chilled, aud the vapour being condensed,
forms c ouds or falls in rain. The strange
phenomenon tami lar to every visitor If the
Cape, knowr aS the laying of the Devils
taOle-clOth on Table Mountain, illustrates
both these &C ions. The mountain arrests
aud turfS upwards the aerial currents, and
III Sc passing over lis elevated and cod
upper surface, their vapour is condensed in
heavy clouds, Which again roll down the
opposite face OF the mouutain but as they
pass dowu come into contact with warmer
air, by which they are once moje di,.ipated
into the form Of invisible v4nour; 50 that
the c oudS pcrpetualy rolling downwards
never come below II certain liur. 1t is
easy 10 perceive tLat forests which keep
cool the surface of the ground aud do not
reflect from their green foliage a. ythiug
like the same amount Of hear that is given
out by a dry, hard soil or rock, must tend
pro tunto to cool the air above them, aud
coust quently to arrest and coHdeuse the
vPpOur 1t contains and bring it dawn in the
form of rain. But this is not their only
nor perhaps their most important opera.
ton upon thu HUMIDITY OF HE air and soil.
They act II : merely us c01deuSerA but as
great reservoirs, especially il warm cli-
mates. They prevent the rapid evaporation
which takes place where the lays of the
sun are admitted directly 10 III sol ; their
roots absorb, and their leaves in turn give
out Il very considerable amount Of mois-
ture and they do on a vast scale very
much the SAM work that reservoirs aud
CmbaukmentS arr compelled to do where
forests are waGting--the Votk, namely, of
preserving and storing up for use duri 6
the dry months tine excess OF water supplied
by The atmosphere during tie roiay season
|CttIopical Or semi tropical climates. Ii is
easy to understand, then, that deuudatiou,
whether by settlement and cultivation or
by fire, exercises a ve,y important eject
upon The charuc er e climate. Dr. Br0wl
believes that some such effect has been
exercised on the climate OF We tern Europe
in the process Of centuries bat the very
great change which has C 'rtainly come over
i in r gard TO temperatnrc-the Writers
Of ancient Italy and ancient Gaul having
been evidently very much more severe than
Onv to which Fame and lay arc now
Gccusiomed-w, u;d appear TO indicate
some other and more general cause an in
djcation conf med by what VIZ Know Of the
tJrmcr existence of glocla' epoch extend
ing almost 20 the shores .: the MeditcrrA-
mean, and Ola previous temperate Climate
extending over Greenland itself. l. Aneri-
ca the evidence collected by Dr.. Brown
does not pUiut TO any general effect as yet
exeIttd by settlement upon The cimpP,
but any one who has traversed q large pat
OF that country, or who has seen uP'Da
map how great a proportion OF 9 snrfnce is
still covered by forest, Can we'll understand
that clearance has not yet been carried so
lar us ssri 'usly TO impair tbs %rninfal! or ST.
rage Of rain, whatever may hive occurred
in particular regions winch have been mOra
thoroughly denudel In ST. Helena aud in
MauIilius the clse appears 10 have been dis
timely different, liquidation lh-re having
veryseriouSly aft c:ed the climate. The same
thing has occurred in Ma leira, and perhaps