(Biot, in the 'Mem. de l'Acad. des Sciences', t. viii., 1829,
p. 39-41.)
Of these three methods* the
p 170
last is the most certain, since it is independent of the difficult
determination of the density of the mineral masses of which the spherical
segment of the mountain consists near which the observations are made.
[footnote] *The three methods of observation give the following results:
(1.) by the deflection of the plumb-line in the proximity of the Shehallien
Mountain (Gaelic, Thichallin) in Perthshire, r.713, as determined by
Maskelyne, Hutton, and Playfair (1774-1776 and 1810), according to a method
that had been proposed by Newton; (2.) by pendulum vibrations on mountains,
4.837 (Carlini's observations on Mount Cenis compared with Biot's
observations at Bordeaux, 'Effemer. Astron. di Milano', 1824, p. 184); (3.)
by the torsion balance used by Cavendish, with an apparatus originally
devised by Mitchell, 5.48 (according to Hutton's revision of the
calculation, 5.32, and according to that of Eduard Schmidt, 5.52; 'Lehrbuch
der Math. Geographie', bd. i., s. 487); by the torsion balance, according to
Reich, 5.44. In the calculation of these experiments of Professor Reich,
which have been made with masterly accuracy, the original mean result was
5.
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