When we consider the situation of the human mind in Nature, its limited plasticity and few channels of communication with the outer world, we need not wonder that we grope for light, or that we find incoherence and instability in human systems of ideas. The wonder rather is that we have done so well, that in the chaos of sensations and passions that fills the mind, we have found any leisure for self-concentration and reflection, and have succeeded in gathering even a light harvest of experience from our distracted labours. Our occasional madness is less wonderful than our occasional sanity. Relapses into dreams are to be expected in a being whose brief existence is so like a dream; but who could have been sure of this sturdy and indomitable perseverance in the work of reason in spite of all checks and discouragements? The resources of the mind are not commensurate with its ambition. Of the five senses, three are of little use in the formation of permanent notions: a fourth, sight, is indeed vivid and luminous, but furnishes transcripts of things so highly coloured and deeply modified by the medium of sense, that a long labour of analysis and correction is needed before satisfactory conceptions can be extracted from it. For this labour, however, we are endowed with the requisite instrument. We have memory and we have certain powers of synthesis, abstraction, reproduction, invention,--in a word, we have understanding. But this faculty of understanding has hardly begun its work of deciphering the hieroglyphics of sense and framing an idea of reality, when it is crossed by another faculty--the imagination. Perceptions do not remain in the mind, as would be suggested by the trite simile of the seal and the wax, passive and changeless, until time wear off their sharp edges and make them fade. No, perceptions fall into the brain rather as seeds into a furrowed field or even as sparks into a keg of powder. Each image breeds a hundred more, sometimes slowly and subterraneously, sometimes (when a passionate train is started) with a sudden burst of fancy. The mind, exercised by its own fertility and flooded by its inner lights, has infinite trouble to keep a true reckoning of its outward perceptions. It turns from the frigid problems of observation to its own visions; it forgets to watch the courses of what should be its "pilot stars." Indeed, were it not for the power of convention in which, by a sort of mutual cancellation of errors, the more practical and normal conceptions are enshrined, the imagination would carry men wholly away,--the best men first and the vulgar after them. Even as it is, individuals and ages of fervid imagination usually waste themselves in dreams, and must disappear before the race, saddened and dazed, perhaps, by the memory of those visions, can return to its plodding thoughts.