Ottumwa tri-weekly courier. [volume] (Ottumwa, Iowa) 1903-1916, 1916-05-23
Studying the Sun
BY Frederic ]. Haskin

sun; the direct light and that reflected
from clouds and the earth being care
fully distinguished.
The Investigations of the suns heat
are made by pyrheliometer, which
has been brought to very high state
of perfection. It's principle Is simple.
A bright metal plate which will absorb
the rays of the sun Is exposed In a
glass case on the roof Of the building.
This plate is connected by wires with
a resistance" in an electrical circuit
in the laboratory. In accordance with
a we'll known electrical law, the heat
increases this resistance, thus affect.
ing the current, which actuates pen.
Thus the variations OF temperatures
are accurately recorded IN the course
of line.
The measurement of the heat that
Is radiated from the earth IS OF far
more importance than you would sus-
pect: for it is chiefly this second
heat that warns our atmosphere. All
heat travels in waves. The suns heat
reaches the earth In very long wave
lengths, which penetrate the atmos'
phere and are absorbed by the earth.
Later this heat Is radiated out again
in short wave lengths which are held
by the atmosphere. A..
This radiation of heat has given rise
to some striking phenomena. 1t has
long been known to mountain people,
for example, that high up on mountain
sides there are belts OF land in which
no frost forms. even when there 10
frost in the valleys below. These
thermal belts" were also long known
to the weather experts; but the first
accurate observations OF them were
made quite recently. The weather
men went to region in the Allegheny
mountains where this phenomenon
was known to occur and established
several stations on the mountain SIDE,
the highest being seventeen hundred
feet above the valley They found
that during the day 1t was four degrees
colder at this elevation than In the
valley. but as soon as the sun went
down this condition began to reverse
itself, and by s o'clock at night the
valley was colder than the mountain
top. This was found to be due to the
reflected heat. 1t warmed the air IN
the valley, which began to rise De-
cause it was lighter. while at the same
time the cold air of the upper slopes
fell. This process continued practlc-
ally all night, the valley filling with
cold air. while heat rose from its bot
tom to warm the mountains. In this
region, it was possible to raise frutc
far up the mountain side: but the
blossoms were always killed by frost
in the valley.
The light of the sun Is measured IN
foot candles. which is unit approx
mately equal to the candle power IN
which electric light Is expressed. The
investigators have found that In jan
uary at noon, when the sun Is shin
ing. It is giving us about four thousand
foot candles OF light, while in June 1t
attains a power of ten thousand foot
candles. Much of this light is reflect
ed from the sky. especially when there
are white clouds in it. The amount
varies from one thousand to three
thousand foot candles. At sunset there
are only one hundred foot candles OF
light. and when the sun Is sixty de-
grees below the horizon, there is one
tenth Of one foot candle. Vet even
in this light large print may be read.
Thus It is seen that the human eye
may be adjusted in single day to
lights varying from one-tenth to ten
thousand foot candles.
An interesting result Of these light
measurements is table which gives
the exact length of twilight at all
times Of the year. This information
has some Immediate practical bearing
in law suits arising out Of collisions.
On the great lakes especially, the
weather men are frequently called up
on to determine whether a certain
hour was within twilight, as the law
provides that boats must show certain
lights at dark.
Although measurements Of solar
radiation have been made in other
countries, those now being carried on
by the government weather bureau are
the most extensive and complete. They
constitute an important American con-
tribution to the worlds scientific
knowledge.