In this memoir the author first deduces a formula upon
geometrical
considerations
alone
, expressing the deviation of a free pendulum (like Foucault’s) in terms of the latitude and difference of meridians, or hour-angle; and this is done (as far as appears) without any reference to the
dynamical
considerations on which Foucault’s formula is deduced, assuming only the inertia of the pendulum. The author’s formula assumes the earth to be a
sphere
. If now, observation should give a slightly different deviation, the author infers that this would be due to the
ellipticity
of the earth; and in vestigates a formula geometrically, to express the ellipticity in terms of such difference; and thus by accurate observations of Foucault's pendulum in different parts of the earth, he conceives the ellipticity might be determined.