l'évolution fondamentale résulte nécessairement de leur dépendence
mutuelle. Toutes les sciences peuvent, sans doute, être ébauchées à la
fois: leur usage pratique exige même cette culture simultanée. Mais
elle ne peut concerner que les inductions propres à chaque classe de
spéculations. Or cet essor inductif ne saurait fournir des principes
suffisants qu'envers les plus simples études. Partout ailleurs, ils ne
peuvent être établis qu'en subordonnant chaque genre d'inductions
scientifiques à l'ensemble des déductions emanées des domaines moins
compliqués, et dès-lors moins dépendants. Ainsi nos diverses théories
reposent dogmatiquement les unes sur les autres, suivant un ordre
invariable, qui doit régler historiquement leur avénement décisif, les
plus indépendantes ayant toujours dû se développer plus tôt."

[7] "Science," says Mr Spencer in his "Genesis," "while purely inductive
is purely qualitative.... All quantitative prevision is reached
deductively; induction can achieve only qualitative prevision." Now, if
we remember that the very first accurate quantitative law of physical
phaenomena ever established, the law of the accelerating force of
gravity, was discovered and proved by Galileo partly at least by
experiment; that the quantitative laws on which the whole theory of the
celestial motions is grounded, were generalized by Kepler from direct
comparison of observations; that the quantitative law of the
condensation of gases by pressure, the law of Boyle and Mariotte, was
arrived at by direct experiment; that the proportional quantities in
which every known substance combines chemically with every other, were
ascertained by innumerable experiments, from which the general law of
chemical equivalents, now the ground of the most exact quantitative
previsions, was an inductive generalization; we must conclude that Mr
Spencer has committed himself to a general proposition, which a very
slight consideration of truths perfectly known to him would have shown