Atlanta semi-weekly journal. (Atlanta, Ga.) 1898-1920, 1916-05-16
STUDYING THE SUN
: BY FRLDEHfc J. HAsKIN.

c.nara+e observations are made of the amount Of
light afforded by the the direct light and that
reflected from clouds and the earth being carefully
distinguished.
The Investigations of the suns heat made by
pyrheliometer which has been brought to very high
state of perfection. principle is simple bright
plate which will absorb the rays of the is
exposed a glass the roof of the building.
This plate connected by wires with resistance"
electrical circuit in the laboratory In accord
ance a well-known electrical law, the heat in
this resistance, thus affecting the current
a pen. Thus the variations of temper
accurately recorded in the course of line
The of the heat that is radiated from
the earth of far Importance than would
suspect it is chiefly this second heat that
our atmosphere All heat travels The suns
heat reaches the earth in very long lengths
which penetrate the atmosphere and absorbed by
the earth Later this heat is radiated out again in
short wavelengths which held by the atmosphere
This radiation of given rise strik-
ing phenomena. 1t has long been known to mountain
people. for example that high up mountain sides
belts land in which no frost forms, even
when there is frost in the valleys below. These
thermal belts also long known the weather
experts but the first accurate observations
were made quite recently. The weather to
a region in the Allegheny mountains where phe-
nomenon was known to occur, and established several
stations the mounainside. highest being 100
feet above the valley. They found during the
day 1t degrees colder elevation than in
the valley; but soon sun went down this
condition began to itself, by o'clock at
night the valley colder than mountain top.
This was found to be the reflected heat It
warmed the air in the valley which to be-
cause 1t was lighter. while at the time the cold
air of the slopes fell. process continued
practically all night, the valley filling air
while heat rose from its bottom to warm the noun
tans In this region it possible raise fruit far
the mountainside; but the blossoms were ALWAYS
killed by frost in the valley.
The light Of the is measured in foot candles
which is unit approximately equal to candle
in which electric light is expressed
tigators have found that in January the
shining 1t is giving foot candles
of light, while in June 1t attains power of 10000
foot candles Much of this light reflected from the
sky, especially when there white clouds The
amount varies from 1000 5000 foot candles At
when the is so degrees horizon there is
print may be read. Thus It is that the human
be adjusted in a single day to lights varying
from one-tenth to 10000 foot candles 90.
An interesting result Of these light measurements
is which gives the exact length of twilight at
all times of the year. This information has i'm
practical bearing in lawsuits arising
collisions. the Great Lakes especially the weather
mon frequently called upon to determine whether
a certain hour within twilight, the law pro-
vides that boats show certain lights at dark
Although measurements Of solar radiation have
other countries, those being carried
on by the government weather bureau the most
extensive and complete. They constitute important
American contribution the worlds scientific know-
edge