All the
properties of a body are modified when taken in small mass; M. Meslin
proves this in a very ingenious way as regards optical properties, and
Mr Vincent in respect of electric conductivity. M. Houllevigue, who,
in a chapter of his excellent work, _Du Laboratoire a l'Usine_, has
very clearly set forth the most interesting considerations on atomic
hypotheses, has recently demonstrated that copper and silver cease to
combine with iodine as soon as they are present in a thickness of less
than thirty millionths of a millimetre. It is this same dimension
likewise that is possessed, according to M. Wiener, by the smallest
thicknesses it is possible to deposit on glass. These layers are so
thin that they cannot be perceived, but their presence is revealed by
a change in the properties of the light reflected by them.
Thus, below fifty to thirty millionths of a millimetre the properties
of matter depend on its thickness. There are then, no doubt, only a
few molecules to be met with, and it may be concluded, in consequence,
that the discontinuous elements of bodies--that is, the molecules--
have linear dimensions of the order of magnitude of the millionth of a
millimetre.
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