An introduction to astronomy: designed as a text-book for the use of students in college. By Denison Olmsted ...

FIGURtCS OF TIlE EARTH-. f
ina the equatorial regions, lcaving bare extcensive regions on tell
one side, and asedllting to a mounltainous clevationl on the otetcr.
O ( cstinatiItg firont tlte known dlimnelsions of the earth and
the, vclocity of its rotationt the a-notllft of tlhe centtriftlgal fotrcc
in (litkerent latitudes, and tihe figure'of equilibriunm whlict Nwould
result, Newton infierred that the earth ltust htav r te frm'lt of
an oblate spheroid bfort tile fliet had been established b)y obscrvation; antd lie assigned nearly the trite ratio of the polart
and equatorial diameters.
1 38. Secondly, the s.2leroidal figure of the earthalb is >oved
by actually mnreastrmiunyg / le Igtk qy a degyee ont the?meidirran; in
d4/e1ni]t latitudes.
WVere the earthl a perfect sphlere, the section of it made by a'
plane passing tllrough its center in any direction wtould b)e a
perfect circle, whose curvature would be equal in all tl alts
but if we find by factual observation tfhat the curvIature of tthe
section is not unlliforl'l, we infer a correspon)di) g; parturt in.
the eartit firom the figure of a pcrfcct spilre. Tliis task of
measuring portions of the meridian lhtas been executed in different countries by means of a systeml of triangles withl aste:lis]hice accurtlacy.'t'.h'I result is, that t]he lengt]h of a degree
iitcrcascs ts we proced from tlec equator toward the polce as
may h}: seen froml the following table'
1'sec3s of olbservation. Latitude, f der......................................................................................
c eru....... O 00' 00" 68.7S32
Pentnsv\vania... 39 12 00 68.896
italy.......... 43 01 00 68.998
France....... 46 12 00 69.054t
Entgland........ 51 29 SITy 69.1 6
Sweden...1.... 20 10 69.'292....................................................................................
Combi'nil Lg tie results of various mneasuretln cts, t~he di'1mensions of ttte terrestrial sphteroid are found to be as follows"'.lEquatorial diameter,.. 7925.308
]Polar diameter,..7898.952
AMean diamteter.. 2.. 71. 3 0
0o Se Day' s Trigont0ometry.. Besse.