C., as to the first definition of the metre. We must
admire the incredible precision attained at the outset by the
physicists who made the initial determinations, but we know at the
present day that the kilogramme they constructed is slightly too heavy
(by about 1/25,000). Very remarkable researches have been carried out
with regard to this determination by the International Bureau, and by
MM. Mace de Lepinay and Buisson. The law of the 11th July 1903 has
definitely regularized the custom which physicists had adopted some
years before; and the standard of mass, the legal prototype of the
metrical system, is now the international kilogramme sanctioned by the
Conference of Weights and Measures.
The comparison of a mass with the standard is effected with a
precision to which no other measurement can attain. Metrology vouches
for the hundredth of a milligramme in a kilogramme; that is to say,
that it estimates the hundred-millionth part of the magnitude studied.
We may--as in the case of the lengths--ask ourselves whether this
already admirable precision can be surpassed; and progress would seem
likely to be slow, for difficulties singularly increase when we get to
such small quantities.
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