gh character of
generality, when enunciated at the end of the eighteenth century,
rapidly gave it such an authority that no one was able to any longer
dispute it unless he desired the reputation of an oddity inclined to
paradoxical ideas.

It is important, however, to remark that, under fallacious
metaphysical appearances, we are in reality using empty words
when we repeat the aphorism, "Nothing can be lost, nothing can be
created," and deduce from it the indestructibility of matter. This
indestructibility, in truth, is an experimental fact, and the
principle depends on experiment. It may even seem, at first sight,
more singular than not that the weight of a bodily system in a given
place, or the quotient of this weight by that of the standard
mass--that is to say, the mass of these bodies--remains invariable,
both when the temperature changes and when chemical reagents cause the
original materials to disappear and to be replaced by new ones. We may
certainly consider that in a chemical phenomenon annihilations and
creations of matter are really produced; but the experimental law
teaches us that there is compensation in certain respects.

The discovery of the radioactive bodies has, in some sort, rendered
popular the speculations of physicists on the phenomena of the
disaggregation of matter. We shall have to seek the exact meaning
which ought to be given to the experiments on the emanation of these
bodies, and to discover whether these experiments really imperil the
law of Lavoisier.

For some years different experimenters have also effected many very
precise measurements of the weight of divers bodies both before and
after chemical reactions between these bodies. Two highly experienced
and cautious physicists, Professors Landolt and Heydweiller, have not
hesitated to announce the sensational result that in certain
circumstances the weight is no longer the same after as before the
reaction. In particular, the weight of a solution of salts of copper
in water is not the exact sum of the joint weights of the salt and the
water. Such experiments are evidently very delicate; they have been
disputed, and they cannot be considered as sufficient for conviction.
It follows nevertheless that it is no longer forbidden to regard the
law of Lavoisier as only an approximate law; according to Sandford and
Ray, this approximation would be about 1/2,400,000. This is also the
result reached by Professor Poynting in experiments regar