y, similar to all other instances of
invention, when the idea arises, tending to become objective.

Otherwise, the differences here pointed out between the two forms of
imagination--esthetic and mechanical--are but relative. The former is
not independent of technical apprenticeship, often of long duration (e.g.,
in music, sculpture, painting). As for the latter, we should not
exaggerate its determinism. Often the same end can be reached by
different inventions--by means differently imagined, through different
mental constructions; and it follows that, after all allowances are
made, these differently realized imaginations are equally useful.

The difference between the two types is found in the nature of the need
or desire stimulating the invention, and secondly in the nature of the
materials employed. Others have confounded two distinct things--liberty
of imagination, which belongs rather to esthetic creation, and quality
and power of imagination, which may be identical in both cases.

I have questioned certain inventors very skillful in mechanics,
addressing myself to those, preferably, whom I knew to be strangers to
any preconceived psychological theory. Their replies agree, and prove
that the birth and development of mechanical invention are very
strictly like those found in other forms of constructive imagination. As
an example, I cite the following statement of an engineer, which I
render literally:

"The so-called creative imagination surely proceeds in very different
ways, according to temperament, aptitudes, and, in the same individual,
following the mental disposition, the _milieu_.

"We may, however, as far as regards mechanical inventions, distinguish
four sufficiently clear phases--the germ, incubation, flowering, and
completion.

"By germ I mean the first idea coming to the mind to furnish a solution
for a problem that the whole of one's observations, studies, and
researches has put before one, or that, put by another, has struck one.

"Then comes incubation, often very long and painful, or, again, even
unconscious. Instinctively as well as voluntarily one brings to the
solution of the problem all the materials that the eyes and ears can
gather.

"When this latent work is sufficiently complete, the idea suddenly
bursts forth, it may be at the end of a voluntary tension of mind, or on
the occasion of a chance remark, tearing the veil that hides the
surmised image.

"But this image always appears s