Pierre weekly free press. (Pierre, S.D.) 1889-19??, 1916-07-13
GLOBES IN NATURE
Why Raindrops and the Planets
and Suns Are Round.
THE FORCES OF ATTRACTION.

As a Crowd Gathers In a Circle Around
an Object of Interest, So Molecular
and GravitationaI Impulses In Mat
ter Act Toward a Center.
Falling rain forms into spherical
drops for the same reason that the
earth has become a g~lobe-namely,
because that is the shape in which the
internal forces of attraction attain Il
balance. In the case of a very large
and massive body like the earth ii is
the attraction of grayitation that CON
trolls the form, but III that Of a small
body like a raindrop it is the molecular
attraction of the inlinitesimal PARTICLES.
The intensity of molecular attraction,
which is the force that holds the CON
ponents of bodies together. is far great
er than that OF the attraction of gravi.
tation, but it is exercised over n com
paratiyely insignificant distance. In
each case, however, the resultant of all
the attractions between The Individual
particles is a force directed toward the
center of MAS.
But by the principle of inertia time is
always required for any force or com.
bination of forces to set matter in mo-
ton. The larger the volume Of matter
concerned the longer will he the time
needed for the internal forces TO group
all the particles Symnletlically around
their onlmon center of mass,
1t is upon this principle that the old
fashioned shot towers are operated.
Molten lead is dropped from IL great
elevation after passing through a sieve
to facilitate its separation into small
masses, and during their downward
flight these masses are rounded into
little spheres by the mutual attraction
OF their molecules, which group them
selves around a common center.
With very large bodies not broken up
into small portions the gravitational
force plays the principal part in shap-
ing them. because gIayitation is cftec
tive at great distances and throughout
vast masses. while cohesion, or moleclI
lar attraction, is extremely limited with
regard to the space over which it acts.
Each molecule attracts ii little group
OF other molecules close around 1t, and
these in turn attract their Immediate
neighbors. Within the space occupied
by a raindrop the molecular attraction
Is the master force and quickly shapes
the mass into a sphere.
And just as a spoonful Of water
thrown from a high tower will descend
IN the form OF one or o round drops
owing to the resultant pull of all its
molecules toward a common center so
the entire ocean If it were flung ont
into open space would become a gigan,
TIC ball Of water rounded into that
shape by the g%ravitational attraction
acting throughout its whole mass.
1t Is ny no accident that all the
planets are spherical. They have
taken that shape as inevitably as a
loose stone rolls down a steep hill
Their forms are not perfect spheres,
they have been subjected to
outside disturbing forces, such as the
centrifugal effects of their rotation on
their axes and the determinations pro
duced by the attraction of other planets
and of the sun. Even the heads of
comets are spheroidal. although they
are believed to consist OF swarms of
small bodies like metcors.
This tendency Of masses. whose com
ponent parts or particles are free to
move among n another, to assume a
globular outline, is c%uriously illustrated
even BY crowds or swarms of sentient
beings. Thus n swarm Of bees when
It gathers close becomes spherical or
spheroidal, since that form is best
suited to inclose the greatest number
Of individuals.
A human crowd certainly would take
q spherical form If its members were
able to choose their positions as freely
IN up and down as IN horizontal space.
Being confined to one level. they ar
range themselves in a circle, which is
the section Of sphere. Garrett r.
N0rvfac an Nnw No,l, a.,. ~