phenomena too curious not to have attracted, from
the beginning, the attention of philosophers, who con-
tented themselves with borrowing from them comparisons
and figures, and the curiosity of searchers for the philos-
opher's stone, who were less disinterested. Might
not a base metal be transformed into a precious one
by means analogous to that which derived a savory
bread from an indigestible paste? Is there not some
powder of transmutation acting like a ferment? Here
we have the question which the alchemists asked
themselves and which naturally they did not solve,
first because it is insoluble, second because though they
were experimenters, they were still more logicians,
believing in the power of the idea, and inclined to sub-
ordinate experiment to it.

It is not that there do not exist in their writings
phrases in which, if one is so inclined, it is possible to
see, like the break of day, the forecast of recent discov-
eries. But in reading these ancient authors we must
always bear in mind that the word with them has often
preceded the idea because of the general mode of
education of the middle ages, and that in the sciences
the idea has almost always preceded the fact. The
word has no value of its own; an idea, so long as it
remains a view of the mind, is always balanced by an
opposing idea; the fact alone is convincing and brings
certainty. But facts are what the alchemists scarcely ever
found on the question of fermentation. The defini-
tions of it which they have given are only obscure or
pretentious paraphrases of the phenomena observed in the
manufacture of wine or of bread. They make allusions
sometimes to the setting free of gas (exaltatio), sometimes
to the fact that the fermented bread can, in its turn,
act as a yeast (immutatio). But as they knew nothing
of the nature of the substance which ferments, nor of

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