Time cannot be thoroughly defined, nor even properly comprehended by mankind, for our personal acquaintance with it is so brief that our longest term is compared to a span, and to 'the grass which in the morning is green and groweth up, and in the evening is cut down and withered.' The ordinary thinker can scarcely carry his idea of Time beyond that small portion of it which he has known, under the name of life-time. The metaphysician classes Time with those other mysteries,—Space, Matter, Motion, Force, Consciousness, which are the Gordian knots of Mental Science.
Time is naturally divided into three most unequal parts,—whereof the Past includes all that has happened until now from that far-distant period when 'Heaven and Earth rose out of chaos;' the Present is but a moment, expended in a breath, to be again like that breath momentarily renewed; the Future is, as the Past,—'a wide unbounded prospect,' an 'undiscovered country,' into which Prophecy itself penetrates but partially, and even then bears back to us but small information; for its language catches the character of a grander clime, and the denizens of this lower earth are incapable of understanding its gorgeous metaphors; the brightness is as blinding as the darkness. We may attempt to pierce the Future by the light which History throws from the Past, but History's record is imperfect; her chronicles are of the rudest and most unreliable character; her most valued memorials serve but to make Past 'darkness visible,' her most ancient registers reach back but a short distance compared with those testimonies which geologists have discovered, and given us veritable 'sermons in stones' about.
The Past is, indeed, scarcely less of a mystery than the Future; even the Present we only know in part, but we do know that the brief term during which man 'flits across the stage' of time ere he goes hence and is no more seen, is of inestimable value. Most of us soon make the discovery that the world has much to teach which there is little time to learn and still less time to apply to good purpose. Ars longa, vita brevis est, is the general expression of human experience.