(Schumacher, 'Astron. Nachrichten', 1830, No. 164, s. 399.) Regarding the
influence of dense masses supposed to lie at a small depth, equal to the
mean height of the Alps, see the analytical expressions given by Hossard and
Rozet, in the 'Comptes Rendus', t. xviii., 1844, p. 292, and compare them
with Poisson, 'Traite de Mecanique' (2me ed., t. i., p. 482. The earliest
observations on the influence which different kinds of rocks exercise on the
vibration of the pendulum are those of Thomas Young, in the 'Philos.
Transactions' for 1819, p. 70-96. In drawing conclusions regarding the
Earth's curvature from the length of the pendulum, we ought not to overlook
the possibility that its crust may have undergone a process of hardening
previously to metallic and dense basaltic masses having penetrated from
great depths, through open clefts, and approached near the surface.
In the astronomical part of the determination of degrees of latitude,
mountain chains, or the denser strata of the Earth, likewise exercise,
although in a less degree, an unfavorable influence on the measurement.
As the form of the Earth exerts a powerful influence on the motions of other
cosmical bodies, and especially on that of its own neighboring satellite, a
more perfect knowledge of the motion of the latter will enable us
reciprocally to draw an inference regarding the figure of the Earth.
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