Evening star., 1941-06-21
Of Stors, Men
And Atoms
Notebook Of Science Progress
In Laboratory. Field
And Study
By Thomas r. Henry.


hope to see in the middle latitude is a
rainbow at noon.
When a man in Southwestern
Colorado wrote to the United States
Weather Bureau few days ago describ-
ing such an experience his letter was
turned over to DR.. William J.
Humphreys probably the worlds fore
most authority on meteorological
curiosities. After a lot of calculations
DR.. Humphreys has just assured the
Coloradan that what he saw was &C
tually a rainbow.
A rainbow is always caused, DR..
Humphreys explained. by sunlight fall
ing through local shower. The water
droplets act as prisms to break up the
white light into its spectrum stretching
from red to violet. The phenomenon
would be impossible unless it rained
while the sun was shining.
Now, DR.. Humphreys explains, half
a rainbow is always below the horizon.
Usually much more than half of 1t Is
hidden and in order for it to be visible
at all it is necessary for the sun to
be fairly low in the sky. This is the
reason that the phenomenon seldom is
seen except late in the afternoon or
early in the morning. BY checking
the exact altitude of the sun at noon
in that particular latitude on the day
when the Coloradan saw the rainbow,
however, DR.. Humphreys found that.
given all other requirements, the tip
extending above the horizon actually
could have been seen.
The Coloradans description added
credence to his story. Under the arch
of the bow, he said, the sky glowed
with a kind of purplish light such as
he never had witnessed before. This
actually would have been the case, DR..
Humphreys concluded. What the man
actually saw was three or four secondary
rainpoWs under the clearly visible one.
Quill iuulll-IOlOICo dlNllSo AL bilN ohJ
very seldom occur singly and the Gov
eminent meteorologist says that he
himself once counted six of them, one
under the other.
But in the secondary rainbows the
red and green wave-lengths of light are
most prominent, often drowning out all
the others and blending together into
a glow which appears purple when seen
through the dusty atmosphere. Rain
bows at noon, Dr. Humphreys said,
would be seen quite frequently in
middle ATTITUDES during the late fall
and winter except that at these seasons
there are very seldom local showers
occurring in bright sunshine. In the
far North they should be seen OCCASION
ally even in summer.
Speaking of rainbows," says DR..
Humphreys, no two persons ever saw
The same one, or one in exactly the
same location. The position of rain
bow depends absolutely on the position
of the observer. 1t will be at the end
of the straight line drawn through
himself from the sun which must be
directly behind him. Two persons of
course see a rainbow at the same time. If
they are standing very close together
the arches seen by both of them are
in approximately the same position and
appear to be identical. In fact, two such
rainbows may overlap each other"
But actually, Dr. Humphreys says, two
persons standing even a few feet apart
see an altogether different rainbow
formed by sunlight falling through
different drops of water. Thus rain
bow is the single thing outside a
persons own body which is absolutely
his personal property. There are no
possible means by which it can be seen
by anybody else unless the person seeing
it leaves the spot where he is standing
when he Immediately gets new rain
bow exclusively his own.
Among the questions frequently re-
ceived by DR.. Humphreys is the dis
tance of q rainbow. To this question
he has a stock answer. 1t depends on
the distance of the local shower
through which the sunlight is falling
Thus a vari-colored arch often is
formed in the spray of garden hose
and one can stick hand in the middle
of it. But If he moves little trying
to touch it he gets an entirely new
rainbow for his pains.
Another question just solved by DR..
Humphreys is whether spring is pos
sible on top of a mountain. 1t required
a lot of complicated calculations to
prove conclusively that such a phe-
nomenon is impossible except at rare
intervals and for very brief periods.
There may, of course, be plenty of
springs short distance below a summit
and springfield lakes are known in high
mountains.
But his calculations show, DR..
Humphreys says, that an actual flow of
water from the upper tip of noun
tain could occur only under conditions
of water storage and atmospheric pres
sure which could be combined in nature
univ nv the rarest sort of accident