The Indianapolis journal. [volume] (Indianapolis [Ind.]) 1867-1904, 1902-11-30
THE EARTH'S ROTATION.
FOucaults Experiment Proving 1t
Repeated in Paris.
New York Tribune.

New York Tribune.
A pendulum zoo feet long was used in
Paris the other day to demonstrate the
theory that the earth rotates on its axis.
The idea originated half a century ago with
Foucault, French philosopher, and ere
ated much excitement among scientific peo-
pie at the time. 1t was one of the most
conclusive experiments ever tried for this
purpose, because the proof presented
TO the eye of everybody who would take
the trouble to watch ii. The repetition oc-
CURED in the tower of the Pantheon, in the
French capital.
One can understand the test a little bet
ter if he imagines it first as being tried at
the north pole, one end of the earth'S axis.
At that point the stars, instead of rising
from one horizon as they do at the equator.
crossing overhead and descending to the
opposite horizon, whirl continually around
the zenith. All that are visible at any one
time remain in sight, hour after hour, if
darkness only permits seeing them. The
whole system rotates Cor appears to ro-
at the terrestrial pole, is straight upward.
Since such distinctions as north, south,
east and west disappear at the pole, the
stars, more especially those low down In the
heavens, may be used as landmarks.
The principle of which Foucault made
use was this: A pendulum, if entirely free
to follow its own inclinations, will persist
in swinging the same plane. If, then, it
be started so that its direction lay first to-
ward one particular star and then to an
other on the opposite side of the sky, and
If the stars themselves were fixed, it's
course should remain unaltered, even If the
platform below the pendulum were moved.
Suppose that the two stars thus selected
were Affair and Procyon. let 1T also be
assumed that the experiment be undertaken
just at noon, and that Affair lay off in the
direction of London, or on the meridian of
Greenwich Procyon would then seem to
overhang one of the Aleutian islands in
longitude $50.
Now, if the earth were stationary and the
skies really moved, then, after several
he Gtn IN 1fvA xxvftl he
the pendulum would not be those toward
which il originally aimed. On the other
hand if the earth moved and the stars
kept still, then the pendulum would swing
the stars themselves would overhang en-
tirely different meridians. AT the end Of
five hours, for instance, Affair would be in
a line with New York city, having moved
westward Is degrees an hour, and Procyon
would be over Irkutsk,- in longitude los
east of Greenwich. The pendulum would
then traverse line which, If duly extend
ed would reach from New York TO Irkutsk
and not the one it followed at first. Were
the pendulum so arranged that il could
leave a trace on the ground underneath it
say by pin point scratching a level bed
of fine Sand-a record of the change of
course Gas regards the earth) would be
left there. At the end of six hours this
track would be exactly at right angles
with that followed at the beginning of the
experiment. Although the plane of the
pendulum's swing would be unchanged, it
would appear 10 terrestrial observer at
the pole to have moved around an imaginary
vertical line just 90 degrees. In twenty
four hours it would go around a complete
circle.
The phenomenon here described can be
duplicated, though less satisfactorily and
conspicuousy, at other points than the
pole, though a site we'll removed from the
equator must be selected Foucault's his
toric test was made in Paris with a wire
200 feet long, an iron globe a foot through,
a pin projecting downward from the lat
ter and little sand TO register the track
In these particulars his experiment was
closely followed in the attempt made few
days ago in the same city. The lines traced
by the pendulum intersect at a point which
would be Immediately under the pendulum
when the latter was still and hanging
straight downward. Thus a system OF
radi was outlined. proceeding from this
central point. If the path taken by the
pendulum at the start were precisely north
and south, then, after. few minutes. a
little deviation to the west of south and
east of north would be detected. The varia-
ton would steadily increase until the plane
of the swing had itself rotated on its axis
AT the pole this would undoubtedly be ac-
complished in twenty-four hours. Foucault
found that in Paris a little longer period
was required.