The Pacific commercial advertiser. [volume] (Honolulu, Hawaiian Islands) 1856-1888, 1856-07-31

e. e. needs no further commentary. Nor will any one who takes
a look at the bleak slopes Of the steep basabic hills back OF our
-tnaoe find difficulty to conceive how a heavy dashinG rain viii
wash away the minutest particle of soil, as soon as 1t forms from
moveafle. humus. soil. left after the clearing of a forest, will, when
situated on a deciivity, be swept ptla away y a ST soon ~ as 1; a a urn am inter- n
leafy roof moderates the force OF the dashlng torrent. ln both
far and the watery deposit when small, viii return 20 the at
mosphere by evaporation, or when large, sweep down in torrents,
over6u the beds of rivers, and pervert by sudden foundations
Into a curse what ought to be a blessing to man. A forest win
~ only by its cool Shade, lessen greatly the evaporation, and
retain What evaporates under its vault, but its canopy will also
moderate the impetus of the falling drops and distribute its de-
forming its floor, by virtue of its great hygroscopic capacity, re
tains for a long time the imbibed liquid, and thereby regulates
the flow of the rivers, preventing their sudden oFeF am ! ms a." IN
yielding them food long after the ain has ceased stn nmnLo
lions of late 80 frequent of the river oder IN II ~ ~ tba MN,
are attributed by experts to the waste oi pre- ~ - nIa - I'll
districts Of Upper Slisia, while it is staten NAT ue ptI III 800 VI
way with the torrential floods which formerly devastated the low
er valies. With regard to the obstacles offered by d thcA otts
70 evanoration. a traveller in South America says: L the
forests the humidity is constant, it exists long after the RAINY
seasor t thTopn~h the whole wear deeply covered with mire. The
on.y means known OF keeping the forest ways dry, IS to give
them a width Of from 26O to $50 feet, that Is 70 say, 10 Gear the
country in their course" A remarkable instance of how run
ming water diminishes by mere evaporation, without falling of,
even with the increase of the yearly quantity OF ram Is related
to us by Boussingault. The metalliferous mountain of Marm-
ate i situated in the province Papayan, IN the midst OF immense
forests. The, stream along which the MINING %orhs are eStto-
Iished, is formed by the junction OF several small riYuets, taking
establishment and is thickly wooded. When Boussinsault visit
ed the place in 1926, he found only a few n era oc cabins IN IN
the most fourishing appearance. 1t was covered with work
gamatting the ores. and a population of nearly 5000 Inhabitants.
1t may be imagined that during these four years an A1Inic cns
quantity of timber had been cut down. not ON! Tor tue COZ
struction of machinery and houses but as fuel ana for manufac-
bic land of San Jorge. But scarcely had two years elapsed, be-
fore a notable dininution of the water in the stream was noticed.
The volume of the water had been measured by the work done
by the machinery, and actual guaging at different times showed
a serious aspect, because at Marmato any diminution in the
quantity of water, which is the moving power, would OF course
be attended with a Proportionate dininution in the Quantity OF
gold produced. AS soon as the diminudon of the stream was
ascertained, a rain guage was set up, and IN the course oil the
than in the first year, although the clearing had gone on. Still
there was no appreciate increase in the size OF the running stream.
n very similar observation has been made on the Island of As
censOn, where an excellent spring at the foot of a mountain,
but reappeared in former abundance, when the mountain was
planted again. Such remarkable effects, arising from the oper--
alton of causes limited to narrow localities, cannot be attributed
to a diminution of rain in the first cited instance there was
even in one year a n uncommonly large fall OF rain undoubtedly
accidental. Undue evaporation only can be assumed as the
Let us now see how forests may effect the absolute quantity
of rain, or precipitate of atmospheric moisture. From the sur
~ ns.a of an aeereCation Of small yesicIes. according
to it's lesser specific gravity, rises steadily from the lower and
warmer. to the upper and colder strata, of the atmosphere. Every
gas, under a given temperature, can only take up a certain max
imum of moisture; when it has reached that, we call it saturat-
ed. When it is saturated, any addition OF yapour WIN De con
densed again to water. The lower strata OF the atmosphere,
being warmer than the upper ones, take up a larger quantity
than the latter consequently these viii De saturatel, wnle tH Lax
former still retain capacity to take up more. "A soon as tnlS
point is reached, all surplus in the upper regions will have the
number of larger ones, whereby they become visible to the eye
as clouds. The more this condensation proceeds, the heavier
the vesicles will become, until their specific gravity exceeds that
of the atmospheric air, when they fall down: In their down
the surplus of the lower strata, which by their contact are sud
denly cooled down beyond their saturation point and reach the
enlin a may yAi Witness So the sight almost s daily i that when a rain
cloud has to pass, in descending through a drier ; stratum tma OF at IT.
own, it dissolves agaa. by evaporation and disappears. The
any strong wind may, tor a limited locality, become a cause OF
disturbance, inasmuch as its impetus will overcome the specific
gravity of a cloud. From these preliminary considerations 1t
seems to be alawful deduction, that any causes, which increase
perature and dryness of the lower strata, will augment the fall
Of rain. Have forests a tendency in either of these ways?
The great source of atmospheric moisture is the vast eXpanse
OF flowing and standing water Tor an uSuIaf Climate IL Is the
paramount one, against which all other sources sink into in
sigaifancy. But different is it with vast tracts of wooded
land in the interior OF a continent, particularly where a high
amount of moisture, exhaled in the negotiating process, will play
an important part, and indeed Humboldt considers it as the
great factor by which forests increase rain.
Far different however is it with regard to the second question:
Do forests contribute to cool the lower atmosphere! A child
knows that a shade affords GOODNESS, by intercepting the rays OF
the sun, and any one, specifically acquainted with the laws Of
as the sapgreen of leaves imbibes the rays of caloric, while a
light one, like sand or limestone, reflects them, and thereby
heats the ambient gaseous medium. The imbibed heat again is
spent in fastening the evaporation of the water contained in the
leaves. But in evaporation of liquid a considerable amount o
caloric is bound as latent heat, which is distracted from the
ambient medium. Pour a drop of ether on your hand and you
Similarly the exhalatiOn of plants. Thus the forests may
operate in a variety Of ways towards reducing the temperature
of the lower strata of atmosphere and Herewith their point 0
saturation.
But these are not the only, perhaps, not even the principal ways
In which forests contribute to fix the atmospheric moisture
Let us consider, how dew originates. a general property of al
heat to the surrounding mediums, and only keep up a STEADY
temperature, when it receives as much, as it gives off. Diferen
bodies possess their quality in a different degree: gases ant
atmospheric airs have least of it, most of all organic substances
particularly Sucn as cOn1Dlu greatest SURFACE WIFI icaSI DtIk
as cotton, wool, feathers. During a clear and calm night, whel
the great generator of caloriC, the sun, has sunk below tht
horizons and no other source of heat is left but. the imperceptibl
one of the proper heat of the earth, all bodies will steadily los
sheat by radiation towards the upper regions of the atmosphere
for these being greatly cooler than the lower ones, will abstrac
heat, without rendering an equivalent. Any fast cooling body
viii, by lowering the saturation point to the surrounding atmos
phere, preciptate the vapory moisture in it; a principle, -upoI
whose application Daniels hygrometer is constructed, and upor
which rests the formation of dew. Dew is only observed during
calm and serene nights whatever obstructs the free commune
cation OF the lower and upper regions of the atmosphere, as
clouds or smoke, prevents the formation of dew, because it les
sens the radiation towards the upper atmosphere. A wind like
wise viii interfere with the formation, as it brings warmer air il
contact with the radiating body. You all will be aware tha
you enjoy the most refreshing sleep during a calm night will
an open starlt sky, while the air becomes sultry and oppressive
when the heaven IS clouded. Grass and leaves being in them
selves strong radiators, will cool the more rapidly, as they have
only q slender communication with the earth, by which thu
acquired sun heat of the latter might be conveyed to them
Thus a thermometer laid on the bare ground, will stand from
ten to fifteen degrees higher. than one suspended between tn
grass. For this reason, grass and trees are covered with dew
when rock and stone are not, and are dripping, when these ar
moist. In tropical countries this phenomenon must necessarily
appear more striking on account of the greater diffusion Q
watery vapor at elevated temperatures. &" In the bivouac Oh
the edge of the forest of Cauca, between the fourth and fifth O
July" says Boussingaut, Z" the night was magnificent never
theless IN the forest, which began at the distance of a few yard
from our encampment; it rained abundanly, by the light of th
unclouded moon we could see the water running from th
branches" Those of you, who frequently have to repair to ou