In order to avoid the uncertainties which respect the centre
of oscillation, it has been proposed by Mr. Leslie, an ingenious
artist of Philadelphia, to substitute, for the pendulum, a uniform
cylindrical rod, without a bob.
Could the diameter of such a rod be infinitely small, the
centre of oscillation would be exactly at two-thirds of the whole
length, measured from the point of suspension. Giving it a diameter
which shall render it sufficiently inflexible, the centre will be
displaced, indeed; but, in a second rod not the (1) six hundred
thousandth part of its length, and not the hundredth part as much as
in a second pendulum with a spherical bob of proper diameter. This
displacement is so infinitely minute, then, that we may consider the
centre of oscillation, for all practical purposes, as residing at
two-thirds of the length from the centre of suspension. The distance
between these two centres might be easily and accurately ascertained
in practice. But the whole rod is better for a standard than any
portion of it, because sensibly defined at both its extremities.
2. The uncertainty arising from the difference of length
requisite for the second pendulum, or the second rod, in different
latitudes, may be avoided by fixing on some one latitude, to which
our standard shall refer.
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