The sensual and spiritual are linked together by a mysterious bond, of which our hearts are distinctly conscious, though it remains hidden from our eyes. To this double nature of the visible and invisible world — to the deep-implanted longing for the latter, coupled with the feeling of the sweet necessity of the former, we owe all sound and logical systems of philosophy, truly based on the immutable principles of our nature, just as to the same source we are able to trace the most visionary and incoherent reveries. A constant endeavour to unite these two elements, so that each may rob as little as possible from the other, has always seemed to me the true end of wisdom.