, 1879-05-31


Cu1cAuo. May 20.-Wlll you be SO kind a. to
explain through tho columns OF your paper how
the daily rotation Of tho earth waslenonstratcd
BY Aome scientific experiments III the erection
and movement Of d pendulum In tho Exposition
Building several years aTaf Dy 50 dom. y0u will
please and INSTRUCT snauy scIiooIrlSoEa.
1The experiment referred to was trst per
formed Feb. 19 1874. Tie pendulum was 1905
feet long, tho tall weighed about 12l pounds,
md 1t nude 5oi swings per fIuur, or ono In etx
seconds, nearly. Tho olanc Of vibration OF tho
pendulum seemed to changu at tho rite Of 10
degrees per hour, the apparent cllango being III
the same direction as tho apparent movement
Of the sun and STARS: viz, from. east, through
eouth, to vest; and from wcst, through north,
to east.
1he change in direction Of the swing Is be-
lteycd 10 be apparent only, not real. The pen-
tlu'um tends to keep on swinging, or vibrating,
In tic sans absolute direction III space. Tho re-
suit Of thIs tendency, with attraction towards
tue Garth while sa turns OIL her axes, Is to mako
tho pendulum vlbrat1 nearly In series Of planes
Of great circles OF the sphere the common diam
etcr Of thcse circles passing through the carth's
centre and being parallel TO the horlzon Of tho
place whcra tho pendulum 6y|ngs.
1t 1nay be that "Schoul-Boy" Will not take
the trouble to picture to himself t!icso condt-
tions, and, II SO, he will fall to understand the
philosophy OF tho phenomenon. II he do rca!-
ize tl.csu conditions mentally, hc will then tlud
ltto difficulty In understanding that the earth's
rotation causes tho plane OF tho meridian Of tho
observer to continuously chAnga its anglo OF
position With reference to these 6ticccssfvelJ oc-
c,tpfed p!a.,cs Of vibration, nti thus makes tho
pendulum 1eetn 10 cllangc the ltrUc.!on Of It's
movement.
The rato at which any point on the esrth's
aurface Is carried eastward bY tho cAsthfs tota.
t1on on her axes Ia nearly equal per hour to 1oiD
miles multiplied into tho cos!tIe of the latitude.
At Chicago, In latitude Az degrees north, tho
hourly motion IL 77J miles nearly, Or $40 yards
per sccond. Ono degree further south 1t Is 3a55,
md ono degree further north 1t Is 373, yarl, pcr
SECOND. II wo take thu particular case ~ which
Tho pendulum was tnade tU vl1rnte lnftinlty
In the plano pf tho meridian at Chicago,
1t Ia easy to see that place further north waa
carried eastward less rapidly, and place further
south was carried eastward more rapidly. than
tho pendulum Itself. The earth thus turned
round under tAs pendulum, causlnE tho pcndu-
ua to scoM to change thu direction Of Its move
mcnt, tho northern swtHg yeeFt1lE to the east,
aud The southern sTlng VecFins to tue Wost.
Tie same fundamental reasoning applies when
the pendulum is swluglns III any othcr direction,
but the undo Of applying II 10 less stmpl0 thnn
iu tne a6ove.naMcd case. ~
i ID degrees be multiplied into tho e!ne Of Tho
latitude At nnJ point, TIC result will b8 tho
amount 9f deviation per atdereal hour at that
place. lhls varies from Is tcxreee at The polo
to zero a. the equator. This ls, Of course, tic
bo little diacrsnt, especially II curreuts Of alr
fwtna) are allowed 10 act on thB pendulum dur
Ing the couraa Of the experiment.
Tho rsstil~nttal Dsath.Doalfne Saver Gas.
~ ths Editor AZ TAs Tr1bune.
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