the
determination of weights and for the decision of physical questions. The
reintroduction of that instrument--for, as we have seen, it had ages
before been employed by the Saracen philosophers, who used several
different forms of it--marked the epoch when chemistry ceased to be
exclusively a science of quality and became one of quantity.

[Sidenote: Theory of oxygen, and the nomenclature.] On the ruins of the
phlogistic theory arose the theory of oxygen, which was sustained with
singular ability. Its progress was greatly facilitated by the
promulgation of a new nomenclature in conformity to its principles, and
of remarkable elegance and power. In the course of time it became
necessary, however, to modify the theory, especially by deposing oxygen
from the attitude of sovereignty to which it had been elevated, and
assigning to it several colleagues, such as chlorine, iodine, etc. The
introduction of the balance was also followed by important consequences
in theoretical chemistry, among which pre-eminently was the
establishment of the laws of combinations of bodies.

[Sidenote: Present state of chemistry.] Extensive and imposing as is the
structure of chemistry, it is very far from its completion. It is so
surrounded by the scaffolding its builders are using, it is so deformed
with the materials of their work, that its true plan can not yet be made
out. In this respect it is far more backward than astronomy. It has,
however, disposed of the idea of the destruction and creation of matter.
[Sidenote: Indestructibility of matter.] It accepts without hesitation
the doctrine of the imperishability of substance; for, though the aspect
of a thing may change through decompositions and recombinations, in
which its constituent parts are concerned, every atom continues to
exist, and may be recovered by suitable processes, though the entire
thing may have seemingly disappeared. A particle of water raised from
the sea may ascend invisibly through the air, it may float above us in
the cloud, it may fall in the rain-drop, sink into the earth, gush forth
again in the fountain, enter the rootlets of a plant, rise up with the
sap to the leaves, be there decomposed by the sunlight into its
constituent elements, its oxygen and hydrogen; of these and other
elements, acids and oils, and various organic compounds may be made: in
these or in its undecomposed state it may be received in the food of
animals, circulate in their blood, be essentia