At the Academy of Sciences at Paris, a memoir was read by Captain
Duperrey, on the experiments made with the invariable pendulum, during
the voyage of the _Coquille_ round the world. He states that various
experiments confirmed the fact of the flattening of the terrestrial
globe, conjectured by several travellers, who had remarked that the
number of oscillations which the pendulum made at certain places,
differed from what had been observed in the extent of the same parallel.
The principal anomalies observed by Captain Duperrey were at the Isle of
France, Mons, Guam, and the Island of Ascension. At the Isle of France,
the invariable pendulum (as had been remarked by M. Freycinet) made in
one day, upon an average, thirteen or fourteen oscillations more than it
ought, supposing the depression to be 1.305, according to the lunar
theory. At Ascension, the acceleration, as noticed by Captain Sabine,
was five or six oscillations, even supposing the depression to be 1.228.
At other stations the difference was almost nothing; and in some, the
motion of the pendulum was retarded. Such differences, Captain Duperry
remarks, between the results of experiment and those given by theory,
cannot be attributed to errors of observation. He is disposed to refer
the cause of the phenomena, with Captain Sabine, to the want of
homogeneousness in the earth, considered as a mass, or to the mere
variations of density in the superficial strata. What tends to confirm
this hypothesis, he says, is, that all observations show that an
acceleration of the pendulum generally takes place on volcanic ground
and a retardation on such as is sandy and argillaceous. A very important
question to ascertain is, whether the flattening is exactly the same in
both hemispheres. From the observations of Captains Duperrey and
Freycinet, it appears that in the southern hemisphere it is 1.291, and
in the northern 1.288; that is to say, it is sensibly the same, or
1.290 in both.
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