There are questions which having been again and again settled, still
from time to time, present themselves for _re_-solution; errors which
having been refuted, and cut up by the roots, re-appear in the next
century as fresh and vigorous as ever. Like the fabled monsters of
old, from whose dissevered neck the blood sprung forth and formed
fresh heads, multiplied and indestructible; or like the weeds, which,
extirpated in one place, sprout forth vigorously in another.

In every such case it may be taken for granted that the root of the
matter has not been reached; the error has been exposed, but the truth
which lay at the bottom of the error has not been disengaged. Every
error is connected with a truth; the truth being perennial, springs up
again as often as circumstances foster it, or call for it, and the
seeds of error which lay about the roots spring up again in the form
of weeds, as before.

A popular illustration of this may be found in the belief in the
appearance of the spirits of the departed. You may examine the
evidence for every such alleged apparition; you may demonstrate the
improbability; you may reduce it to an impossibility; still the
popular feeling will remain; and there is a lurking superstition even
among the enlightened, which in the midst of professions of
incredulity, shows itself in a readiness to believe the wildest new
tale, if it possess but the semblance of an authentication. Now two
truths lie at the root of this superstition. The first is the reality
of the spirit-world, and the instinctive belief in it. The second is
the fact that there are certain states of health in which the eye
creates the objects which it perceives. The death-blow to such
superstition is only struck when we have not only proved that men have
been deceived, but shown besides how they came to be deceived; when