15—5.
SHORT—TIME INTENSITY FLUCTUATIONS 347
the air pressure is greater, there are more atoms present to ,,absorb
the rays and the intensity decreases. It may be concluded that
the cosmic rays have come from beyond the earth’s atmosphere.
_The âaromez‘er eecz‘ amounts to approximately one or two percent
per centimeter of mercury.
.
"
'
After the intensities of the cosmic rays have been corrected for
barometric pressure, it is found that the average value is essen—
tially constant at a given locality.
_
’
There is, however, a very small variation of the mean intensity,
amounting to approximately 0.3 per cent, which follows sun time
but has its maximum in the middle of the morning hours (there is a
,
phase
Several theories haVe been proposed to
account for this diurnal variation, one of which assumès that'the
changes are due to uctuations _in the earth’s magnetic eld. C
There is,…also, a stillsmaller variation of the mean intensity,
"
of approximately 0.03 per cent, which follows star time. It has
',
been proposed
9
that this diurnal variation is due to the moti0n
’
-
of the earth With the rotation of the galaxy and, hence, that cosmic
rays originate from some region outSide'our galaxy.
_'
15—5.
Short—Time Fluctuations in Intensity.—When examined
over comparatively short time intèrvals, the'intensity
of coSmic
rays is found to uctuate around the average value in a random
manner;
The deViationsfr0mthemean' areSometimeS large, and
.
sometimes small. They “range about =the mean according to the
Maxwellian distribution law;-" alawWhich}deals With—large numbers"
of individual particles. ., This suggests that
are of a
_
granular nature,
of
rather - '
'
than in a
-
‘
_’
The amOunt of the
of_ the observed—«cosmic ra“yihtensity at a givenlnstantabouttheaveragevaluemay
to
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rar Par—) — ‘
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