The Washington times. [volume] (Washington [D.C.]) 1902-1939, 1919-05-18

results obtained at these three stations
separated by q distance OF several thou
sand miles were the same, when nearly
simultaneous observations were made and
showed from day to day the same varia-
lions OF the solar constant, is proof that
the variations are true solar variations and
do not owe their origin TO VARYING local
conditions within our own atmosphere.
There Is. according 70 Dr. Abbot, two
fold variation in the solar radiation. There
Is, FIRST q variation Of long period with a
range of from to 5 per cent during the
sun-spot cycle, and, secondly. q short IT.
regular variation that runs its course In
intervals of few days. weeks or months,
with a range that is usually between and
7 per cent and occasionally becomes as
high as 10 per cent The first variation is
believed to be a direct result, and the sec
ond variation an indirect result, Of the
periodic increase and decrease of solar
activity during the sunspOt cycle. As the
sun-spOt cycle itself Is irregular and com
pick, Il is to be expected that the result
ing changes in terrestrial weather condi-
tions would also be of a complex nature.
II is well known how necessarily doubt
full are weather predictions. depending as
they do upon many different local condi-
tions, such as direction Of prevailing
winds position relative to large bodies OF
water. elevation above seaIeVel and many
other factors The effect Of all these local
conditions may mask to q great extent the
effect of changes in the intensity of the
solar radiation, which are also irregular
and complex, depending. as they do, upon
many changes of an irregular and complex
nature within the sun itself.
As Is we'll known, the sun rotates on its
axis In an approximate period OF twenty
seven days, though equatorial regions or
the sun rotate more rapidly than polar
regions The difference in the periods OF
rotation of sun-spots sometimes amounts to
a number of days, depending upon their
solar latitude. If there is. temporarily, a
hot and cold hemisphere of the sun, 1t will
show its effect in terrestrial weather
changes that have a period equal to that
of the suns rotation on its axis, or twenty
seven days.
Two weeks of increased intensity OF
radiation will be followed by two weeks
of decreased intensity of radiation, as the
hot and cold hemispheres of the sun are
alternately turned toward the earth.
In the year 1915 there was Just such
strongly marked variation in the solar
radiations, which continued for several
solar rotations, but finally diminished and
disappeared. To show the irTegularity and
completely of the solar changes. the varia-
lions in solar radiatiOns for 1916 were
radically different from those for 1915.
The twenty-seven day periods Of the year
before were no longer present. A strongly
marked periodicity of three and One-halt
days appeared instead.
The years 1915 and 1916 were near the
sun-spot maximum period The variation
in the solar radiation has no definite
periodicity of short interval. then, that
persists Ifrom year to year. Each year is
a law unto itself yet with well-marked
practicable effects upon terrestrial weather
conditions in spite of the irregular and
complex nature OF the changes.
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