Evening star., 1953-08-21
Space Between Planets
Not Absolute Vacuum
Dust Particles Measure
l,000th Of q Centimeter
By Thomos R. Henry

Space between the suns planets Is
not complete vacuum.
It weighs q little more than a SEX
tr1llionth Of an ounce per cubic cent?
meter. This Is due to dust particles
averaging less than a thousandth of
centimeter in radius and to elemental
particles-electrons and protons-shot
from the surface of the sun.
This is the conclusion of three Swiss
astronomers, H. Siedentopf, A. Behr
and H. Elasser. from analysis of the
zodiacal light at research station on
the summit of the Jungfrau, one of the
highest points in the Alps
This extremely faint, nebulous light
which appears over the western hori-
zon just after twilight and in the east
before dawn is, they assume, due to the
reflection of sunlight from the infini-
tesimally minute particles floating in
solar system space outside the atmoS-
pheres of the planets.
Analysis showed that some of this
light is in the condition known as "po-
larized" which would be the case if it
were reflected from the elemental par
ticles. The rest is ordinary light, such
as would be reflected from dust par
ticles.
Method Explained.
BY comparing the intensity of the
two kinds of light they were able, they
report in the British scientific journal
Nature, to determine the numbers of the
different kinds of rejecting surfaces.
The counts are somewhat less than
had been anticipated. This almost
empty space is what must be traversed
If man ever achieves interplanetary
travel.
The Swiss astronomers found, how
ever, that the So-called "GegenSchein,"
the nebulous light seen after twilight
opposite the sun, is probably composed
of particles with about 80 times the
density of free space. This relatively
dense dust is located about SO, 900 miles
from the top of the earth's atmosphere,
and perhaps belongs to the earth's FAM
lily. It recently was described by Rus
sian astronomers as "the earth's tail"
A tree that maintains armies of fierce
ants to protect it's foliage from other
insects, browsing mammals and men is
the AZtec'S hoitZmamaXalli, or bull horn
acacia.
Its branches are covered by thousands
of large, hollow, curved horns which
grow in pairs like the horns of a bull
Between each pair small leaf sprouts.
It's stem SecreteS nectar SO abundantly
that it sometimes dripS on the ground.
Upon the sides of each leaf grow mi
mute, golden, pear-Shaped eXcrescenceS
full of oils and proteins.
Ants Inhabit Horns.
Inside every horn is a small colony OF
slender black or pale-yellow ants. They
feed on the nectar. They pluck the little
excrescences and store them inside the
horns for their larvae. These ants are
belligerent biters that throng to the
treess defense whenever it is disturbed.
This was interpreted by early natu-
raliSts as mutual defense pact between
tree and insect. The horns protect the
ants. The ants protect the leaves. Slml-
lar trees are found throughout Central
America and northern South America.
The ants live an abundant life during
the wet season. The acacias wither
during the dry season and the insects
perish by millions. Enough always sur
vive, however, to start new colonies as
soon as the rains start.
The defense is especially effective
against depredations of other ants, such
as leaf cutters. Men and cattle also
dread the bites of the ant hordes.
The phenomenon first was observed
by Francisco Hernandez, Spanish physl-
clan sent to Mexico in 1870 by Philip II
to study the resources of the country.