There is not, perhaps, a more painful exercise of the mind than that of treading, with weary and impatient pace, the entire round of thought, and arriving at the same conclusion for ever; then setting out again with increased speed and diminished strength, and again returning to the very same spot - of sending all our faculties on a voyage to discover, and seeing them all return empty, and watch the wrecks as they drift helplessly along, and sink before the eye that hailed their outward expedition with joy and confidence.