Evening star. [volume] (Washington, D.C.) 1854-1972, 1929-07-18
AIRS WATER VAPOR
INFLUENCES HEAT
Changing Quantities of Mois-
ture in Atmosphere Lowers
and Lifts Temperature.
BY Il. c. WILEY,
Associate Professor Of Chemistry. Univer

Of Maryland
We live at the bottom of q sea. It Is
sea of air. The fact that we cannot
see II and feel IT only when 1t Is in mo-
ton renders us somewhat careless of
its extreme Importance. II we stop TO
think for q minute, however. we will
realize its tremendous Importance for
without II all OF the animal life on the
globe would perish in very few min
utes.
The atmosphere at the present time
is composed Of nitrogen, oxygen, water
vapor and carbonic acid gas. Probably
In past ages when the globe was hot
and before animal or plant life ap-
peared the atmosphere contained much
more water vapor or steam than 1t does
at the present time. 1t also may have
contained more carbonic acid gas.
There was more water vapor because
the surface of the earth was so hot that
as soon as rain fell It was Immediately
driven of as steam. Since this was the
case the water which Is now in oceans,
lakes and streams was In the atr1os-
phere. Think Of the tremendous thun-
der storms which must have occurred
In those days aeons ago, when half the
water In a lake the size of Lake Su-
perior fell from the clouds in few
minutes. Think Of the awful peals Of
thunder and the vivid flashes of forked
lightning when this tremendous shower
of hot rain fell on the hot rocks. The
effect was to cool them suddenly and
thus shatter them and to certain ex-
tent dissolve them, thus laying the foun-
dalton for a soil upon which much later
plants could grow.
But time has cooled the globe. It's
surface Is no longer hot, The atynos-
phere Is more kindly.
Eject Of Dry Heat.
The higher the temperature the more
water vspor the air can hold. The air
at zero can hold only one-tenth as
much water as the air on hot Summer
day. We often hear II said Yes 1t IS
warm out In Kansas but you do rot
feel the heat out there. It Is q dry
heat" Now this may be true. for one
will not feel as much discomfort from
a high temperature II the air Is so dry
that the Precipitation OF the body dries
rapidly and thus cools the body. When
water evaporates 1t takes up neat.
Every one has felt the chill caused by
stepping out of the bath tub when the
body is wet. AS soon as the body is
dry the chilly feeling disappears. 30
nature hiss prepared an automatic cool
ing system for the body. When the
temperature Is high the sweat glands
open and water Is poured out on the
surface Of the skin, The evaporation
of this water cools the skin. MOVING
air coming in contact with the drenched
skin hastens the rate Of evaporation
and hence the rate Of cooling. For TINS
reason electric fans and natural breezes
make a high temperature more bear
able. They really cool the BODY.
In certain hot countries and even IN
the southern part Of the United STATES
water for drinking purposes Is often
kept in porous lars. The water from
the inside slowly seeps through the
porous walls and evaporates on the
outer surface and thus cools the water
within. The Army canteen Is inclosed
In a porous cloth which when wet coos
the water inside by using zip the neaI
needed for evaporation. The ground IS
cooled bv even a warm rain since heat
is taken from the ground to evapora'e
some of the water falling on II.
Moisture During Snow.
We sometimes hear 1t said, Yes, It Is
cold out in Montana, but II Is airy
cold. You do not feel it, Now II Il
doubtful If this is true. If there Is snow
IN the ground the air is saturated with
moisture. It. is probably true that when
the thermometer stands at 10 degrees
above zero that there Is very little dlI-
ference in its moisture content al OH
ferent places in the United States. TINS
is because cold air will hold only very
little water anyhow. SO the next tinle
YOU hear any one say that the colo Is
not felt because it is a dry cold you
can tell them that all cold Is airy. Inc
u.;rd 81 course. would make one feel
cold, because II would rapidly carry
away body heat.
In summer We often see water col"
lectinr on the outside of water pipes
which carry running water. II Is SAID
that the pipe is sweating 1t Is
thought by some that this water &C
tually comes from the inside OF the pipe
through tiny holes and thus col!ecIS on On
the surface. If this were true wafer
nine should sweat in Winter as well as
Summer. 1t will be noticed. however,
that only pipes carrying water that IS
actually running sweat" that is pipes
which are much colder than the sur
rounding atmosphere. What really nap
mems is that the water on the OUTSIDE OF
the pipe does not come from the INSIDE
of the pipe at all. but comes from tne
atmosphere and is condensed on IL De,
cause the water pipe is cold. Any colo
object will gather water on its sur
face in Summer in the same way. A
cellar is often damp in Summer not be-
cause water runs into it from the sur
rounding soil, but because the air en-
tering it from the outside is cooled and
deposits water. Such a celler will slowly
dry out In Winter, because the air en-
tering 1t is heated somewhat and taxes
up moisture.
wherever 1t exists whether as ice
snow or water itself is always slowly
evaporating. We might say 1t is slowly
transported by the wind somewhere else
This transportation Of water is on an