Such a standard, roughly
constructed, and exposed to all the injuries of weather and time,
offered very slight guarantees either as to the permanence or the
correctness of its copies. Nothing, perhaps, can better convey an idea
of the importance of the modifications made in the methods of
experimental physics than the easy comparison between so rudimentary a
process and the actual measurements effected at the present time.
The _Toise du Chatelet_, notwithstanding its evident faults, was
employed for nearly a hundred years; in 1766 it was replaced by the
_Toise du Perou_, so called because it had served for the measurements
of the terrestrial arc effected in Peru from 1735 to 1739 by Bouguer,
La Condamine, and Godin. At that time, according to the comparisons
made between this new _toise_ and the _Toise du Nord_, which had also
been used for the measurement of an arc of the meridian, an error of
the tenth part of a millimetre in measuring lengths of the order of a
metre was considered quite unimportant. At the end of the eighteenth
century, Delambre, in his work _Sur la Base du Systeme metrique
decimal_, clearly gives us to understand that magnitudes of the order
of the hundredth of a millimetre appear to him incapable of
observation, even in scientific researches of the highest precision.
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