New-York tribune. [volume] (New York [N.Y.]) 1866-1924, 1902-11-09
THE EARTH'S ROTATION.
FOUCAULTS EXPERIMENT PROVING IT
REPEATED IN PARIS.


hall century ago with Foucault, a French
philosopher, and created much excitement
among scientific people at the time 1t was one
OF the most conclusive experiments ever tried
for this purpose, because the proof was pre-
scented To the eye Of everybody who would take
tn trouble TO watch it. The repetition occurred
IN ne tower OF the Pantheon in the French
ca i,aL
one can understand the test a little better il
DE- imagines it first as being tried at the North
1oier one end OF the earth's axis. At that point
the stars, instead Of rising from one horizon as
iaey 90 at 'He equator crossing overhead and
-1scending TO the opposite horizon, whirl con-
tnually around the zenith. All that are visible
al any one time remain in sight hour after hour
If darkness only permits seeing them. The whole
sy stem rotates Cor appears to rotate around the
pole OF the heavens, which, at the terrestrial
pole' as straight upward. Since such distinctions
as north, south, ca st 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: pendulum, if entirely free to follow its
own inclinations. win persist in swinging in the
same plane If, then, ii be started so that its
direction lay first toward one particular star and
then to another on the opposite side of the sky
and If the stars themselves were fixed its course
should remain unaltered, even if the platform
beloW the pendulum were moved. Suppose that
the two stars thus selected were Affair and
trocyon. Let il also be assumed that the ex-
pertinent be undertaken just at noon, and that
affair lay on in the direction of London or on
the meridian OF Greenwich. Procyon would
then seem to overhang one of the Aleutian Isl
ands in longitude $50
Now, If the earth was stationary and the skies
really moved, then. after several hours the stars
in line with the path of the pendulum would not
be those toward which it originally aimed. On
the other hand, if the earth moved and the stars
kept still, then the pendulum would swing be
tween Attain and Procyon as before but the
stars themselves would overhang entirely differ
ent meridians At the end Of five hours for in
stance Affair would be in a line with New York
City, having moved westward j. degrees an
hour, and Procyon would be over Irkutsk in
longitude 1O5 east OF Greenwich. The pendulum
would then traverse line which if duly ex-
tended, would reach from New York 10 Irkutsk |
and not the one il followed al first. Were the
pendulum so arranged that il could leave a trace
on the ground underneath it-say, 10y q pin point |
scratching a level bed Of fine sand-a record of !
the change Of course (as 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 il would appear 10 a ter /
restrlal observer at the pole 10 have moved
around an imaginary vertical line just 80 de- |
grees. In twenty-four hours il would go around |
a complete circle.
Inc phenomenon here described can be dupl-
Gated, though less satisfactorily and conspicu- |
ously, at other points than the pole, though q
site well removed from the equator must be Sc
lectec- Foucaut's historic test was made in
Paris with wire 200 feet long an iron globe a |
foot through, pin projecting downward from
the latter, and little sand to register the track
In these particulars his experiment was closely
followed in the attempt made a few days ago in
the same city. The lines traced by the pendulum
intersect 81 a point which would be Immediately
under the pendulum when the latter was stil
and hanging straight downward. Thus a sys-
TEN Of radii was outlined, proceeding from this
central point. If the path taken by the pendu-
lum al the start were precisely north and south
then, after few minutes, little deviation to
the west Of south and east Of north would be de-
tected. The variation would steadily increase
until the plane Of the swing had itself rotated
on its axis. At the pole this would undoubtedly
be accomplished in twenty-four hours Foucault
found that in Paris little longer period was
required.