Omaha daily bee., 1909-11-07

ming BAN is then said to rotate, or turn
about an axis, every point in it and on it.
except those on the axis itself, moving in
a true circle of it's own. The center of
each OF the circles is on the axis Of revo-
luton at the foot of the perpendicular
dropped to 1t from the given point. The
points farthest away from the axis are said
to lie on the equator; they form the cir
conference of a circle obtained by cutting
the sphere by a plane through It's center at
right angles TO its axis
1t is evident that all the points In and
on the earthly sphere must move together
In such a way that their relative positions
are not changed nor the sphere distorted.
Hence, while they all rave the same angu-
lar speed about the axis, that is, they all
run the circuit Of their own circles in the
same time, their linear speed, their miles
per hour, must depend upon their distance
from the axis. Thus at the equator every
point moves about 24.OOO miles in twenty
four hours, that is. about a thousand miles
an hour. Omaha is about 5000 miles from
the earth's axis, and rotates therefore at
the rate of about $50 miles an hour. As the
poles are OF the axis itself, they do not
rotate at all. their linear speed is zero.
This. therefore is the first reason why
they are called singular points.
Effect of Rotation.
The consequence Of this immobility is a
total loss Of the so-caIed centrifugal force.
This force is the apparent tendency Of a
point to recede from the center OF revolu-
ton; It is in reality a case Of inertia, ac-
eording to which It tends to retain it's d.
rection and remain on the tangent line.
At the equator this tendeney Is a maxi
mum. and amounts TO l-2S9th Of the gravi
rational attraction. So that the weight OF
bodies Is lessened there by one pound out
OF every 29. AS a consequence the NOV
] able constituents Of the earth's surface, the
air and water, have receded from the axi:
and approached the equator, and have
there Accumulated in a ring Of matter thir-
teen miles thick. The equatorial radius OF
the earth Is therefore thirteen miles longer
than the polar radius. This difference be-
tween the radli of different parts Of the
earth's surface is a gradual one. The polar
radii are the shortest, and the rest In
crease in length gradually until we reach
the equator. so that a meridian section of
the earth is nearly a true ellipse, With its
minor axis running through the poles and
its major axis In the plane OF the equator
The poles Of the earth are therefors
unique in two respects; they do not rotate
ana they are nearer the eaftn cenNei
than the other parts Of the surface. Fol-
both reasons the weight OF bodies Is q
maximum at the poles. It is one pound
out Of every 100 greater than az thS
equator.
These results have been obtained princi-
paIy by means Of the pendulum. w,
know that gravity is the only force tina
moves a pendulum. and hat the time 4
takes to complete a vibration is absolut ~
constant as long as the force Of gravity
and the length Of the pendulum are tn
same. BY transporting the same pendulum
therefore TO various parts Of the earth
surface, We can determine the variation o
gravity, and nus find the shape OF th'
earth. This has been done already in 5,
many places that we have a pretty aoour
ate knowledge Of the shape Of the earth