profonde:
C'est prendre l'horizon pour les bornes du monde.

(To fancy all known is an error profound,--
The sky-line mistaking for earth's utmost bound.)

The idea expressed in this distich is so self-evident that we might
almost characterize it as trite. Yet the history of every science marks
many eminent men, of superior intelligence, who have been arrested in
the way of progress by a wholly contrary opinion, and have very
innocently supposed that science had uttered to them her last word. In
astronomy, in physics, in chemistry, in optics, in natural history, in
physiology, in anatomy, in medicine, in botany, in geology, in all
branches of human knowledge, it would be easy to fill several pages with
the names of celebrated men who believed science would never pass the
limits reached in their own time, and that nothing remained to be
discovered thereafter. In the army of wise men now living it would not
be difficult to name many distinguished scholars who imagine that, in
the spheres whereof they are masters, it is needless to search for
anything new.

It may be unbecoming to talk about one's self, but as, on the one side,
some have done me the honor to ask what I think of certain
problems,--while, on the other side, I have been more than once accused
of busying myself, in a rather unscientific way, with certain vague
investigations,--I will begin by acknowledging that the maxim contained
in the two verses of my motto has been the conviction of my whole life;
and if, from my callow youth until this very day, I have been interested
in the study of phenomena pertaining to the domain of inquiries called
occult, such as magnetism, spiritualism, hypnotism, telepathy,
ghost-seeing, it is because I believe we know next to nothing of what
may be known, and that nearly everything still remains to be
apprehended; for I believe the thirst for knowledge is one of our best
faculties, the one most prolific, without which we should still be
dwelling in an Age of Stone, inasmuch as it is our right, if not our
duty, to seek the truth by all the methods accessible to our
intellectual powers.

It is for this reason that I published among other things, in the course
of the year 1865,--now a quarter-century past,--a treatise entitled
Unknown Natural Forces, and touching certain questions analogous to
those which are to occupy our attention in this paper; and so I ask my
readers to note the following quotations therefrom, as an