s
meant that they have not become freed from the first state. But for
psychology they are different neither in their origin nor in their
nature from those scientific hypotheses that, subjected to the power of
reason or of experiment, have come out victorious. Besides, in addition
to abortive hypotheses, there are dethroned ones. What theory was more
clinging, more fascinating in its applications, than that of phlogiston?
Kant[115] praised it as one of the greatest discoveries of the
eighteenth century. The development of the sciences is replete with
these downfalls. They are psychological regressions: the invention,
considered for a time as adequate to reality, decays, returns to the
imaginative phase whence it seems to have emerged, and remains pure
imagination.

IV

Imagination is not absent from the third stage of scientific research,
in demonstration and experimentation, but here we must be brief, (1)
because it passes to a minor place, yielding its rank to other modes of
investigation, and (2) because this study would have to become doubly
employed with the practical and mechanical imagination, which will
occupy our attention later. The imagination is here only an auxiliary, a
useful instrument, serving:

(1) In the sciences of reasoning, to discover ingenious methods of
demonstration, stratagems for avoiding or overcoming difficulties.

(2) In the experimental sciences for inventing methods of research or of
control--whence its analogy, above mentioned, to the practical
imagination. Furthermore, the reciprocal influence of these two forms of
imagination is a matter of common observation: a scientific discovery
permits the invention of new instruments; the invention of new
instruments makes possible experiments that are increasingly more
complicated and delicate.

One remark further: This constructive imagination at the third stage is
the only one met with in many scientists. They lack genius for
invention, but discover details, additions, corrections, improvements. A
recent author distinguishes (a) those who have created the hypothesis,
prepared the experiments, and imagined the appropriate apparatus; (b)
those who have imagined the hypothesis and the experiment, but use means
already invented; and (c) those who, having found the hypothesis made
and demonstrated, have thought out a new method of verification.[116]
The scientific imagination becomes poorer as we follow it down this
scale, which, however, b