The Pacific commercial advertiser. [volume] (Honolulu, Hawaiian Islands) 1856-1888, 1878-07-27

ODbeu Vi NdpOTs We unu u RTcdl uluEudt
ra Ige of temperature. In South Central Africa
Livingstone found al average range of about forty
eight degrees between the thermometer early in the
morning and at noon. In Central Australia the
daily range averages from forty to fifty degrees. In
the Desert of Sahara. which we naturally associate
with the idea OF overpoweriBg heat, the cold at night
is often painful to bear, and is sometimes sufficient
for the formation of ice. How different would oar
mild Hawaiian climate be but for the abundant sup
ply of this invisible vapOr. Says TynialI "No
doubt Can exist of the extraordinary opacity of this
substance TO the rays of obscure heat; particularly
such rays as are emitted by the earth, after being
warmed ty the sun. Aqueous vapor is a blanket
more necessary to the vegetable life of England than
clothing is to man. Remove for a single summer
night the aqueous vapOT from the air which over
spreads this country, and you would a~ssuredly de-
stroy every plant capable of being destroyed 10y a
freezing temperature. The warmth of our fields and
gardens would pour itself unrequited into space. and
the sun would rise upon an island held fast in the
iron grip of frost. The aqueous vapor constitutes n
local dam, by which the temperature of the earth's
surface is %deepened; the dam, however, finally over
flows. and we give TO space all that we receive from
the SUM-
In stating that aqueous vapor is opaque to heat
We imply the fact that it greedily ahsOrbs the heat
which il fails to transmit; and in this connection we
would notice that the radiant power of a yapOr is
proportional to its absOrbant power. IL is estimated
that an atom OF aqueous vapOr will absorb or radiate
he t with sixteen thousand times the energy of an
atom of air. The fact of this p%rOdigious radiaring
power plays n very important part in accounting for
ciuulS anu ram. II sun raises EhSt quantities Vi
vapOr from the equatorial ocean. This ascending
column OF invisible yapor is protected on all sides hy
the VapOr above it, and until il rises TO n consider
able hight its condensation is rendered difficult. At
length, when there is no longer n protecting screen
above it, the vapOr discharges its heat into space,
end this in a large measure ~ex plaIns its condensation
ard consequent descent IN torrents of rain. Tyndall
be. utifully describes a cumulus cloud rs . the visi-
Bile capital of an invisible column of saturated air.
The formation of dew is "a subject too interesting
to pass by in this connection. The aqueous vapor,
though so good n radiator, is surrounded by more
than a hundred times its own volume of atmospheric
air, whose heat as well as its own must be discharged
by the vapor before he latter can become chilled to
the point of condensation. This enables good solid
radiators at the earth's surface TO give up their heat
much faster than the vapor, aud when thus chilled TO
become condensers of the vapOr Immediately i'll con-
trct with them, while that which is a few teet above
their surface still retains its invisible gaseous form.
Whatever, therefore, favOIs the radiation of the heat
of these bodies and the undisturbed contact of the
vauor with them promotes the condensation of the
vapor and the consequent formation of dew. "A
Gear sky and calm but damp atmosphere all the
books tell US, is necessary for its copiOus formation.
Careful experiments show that the ground Is seldom
more than three degrees colder, at night, than the
air Immediately above it, and that all good radiators
tend to preserve this constant difference in tempera-
ture between themselves and the air in contact with
them. Grass is one of the best radiators of heat and
at the same time a very poor conductor. When
there is no cloud or tree or other obstacle in the way
it radiates heat into space, and, unable to restore
this loss from the earth, it becomes rapidly chilled.
The air Immediately surrounding the grass, and. as
it were, held prisoner, is chilled by contact with ii.
Again, the grass, ever seeking to maintain the con-
slant difference of three degrees between its own
temperature and that of The air about it, falls in tenn
perature, and again the air is chilled. Thus, by g
series of actions and reactions, the grass and stratum
of air Immediately in contact with il are chilled TO a
pOint far below that of the air n few feet above. A
difference of eighteen degrees has often been observed.
Thus the grass takes from the air its burden of
aqueous vapor, and by condensing it to water
maintains its own life. What a beautiful ndapta-
ton of means to an end is here exhihited-the
grass causing the dew and the dew nourishing the
grass There is no surer way of diminishing the
quautity of dew formed in n given district than by
allowing cattle and sheep TO destroy the lorg grass
and other vegetation which act as cOndensers of
the aqueous vapOr.
Overstocking a pasture is the most suicidal policy,
rs it seriously interferes with the very source of
moisture which is to keep the grass alive. Did time
permit, we might show that the rainfall of a dis
trict is greatly affected by the extent of the wood
land. and that cutting down the trees is a crime
against the physical life of n country. If we per-
sst in the defiance of Natures clearly established
laws in allowing the destruction of the trees of our
once beautiful forests and the grass of our once
verdant plains and hillsides, we invite upon our
selves the inevitable penalty which will slowly hut
surely transform these beautiful Islands into a dry
an1 arid waste In this matter LET us heed the