_Connection of this Science with our own personal Interests._--The importance of mental science is evident not only from its relation to other sciences, but from the relation it sustains to man and his higher interests. Some sciences interest us as abstractions--merely speculative systems of truth; others as realities, but of such a nature, and so remote from the personal interests and wants of the race to which we belong, that they make little appeal to our sensibilities. Thus it is with mathematical and astronomical truth. The heavenly bodies, whose movements we observe, hold on their swift silent way, in the calmness of their own eternity, regardless of man and his destiny, even as they rolled ages ago, and as they will ages hence. What have we to do with them or they with us? We watch them as they hold their course through the deep firmament, as children, standing on the sea-side, watch the distant snowy sail that glides silently along the horizon, afar off, beautiful, unknown. So sail those swift ships of the firmament, and only he who made them knows their history. _Psychology in contrast with other Sciences in this respect._--But when we come to the study of ourselves, and the laws of our own intelligence, our inquiries assume a practical importance which attaches to no other departments of truth. It is no longer the sail dimly visible on the far horizon, but our own conscious being that is the object of thought. The question no longer is, Whence comes that swift ship, and whither goes it, but, What am I, and whither going; what my history, and my destiny? This mysterious soul which animates me, and is the presiding divinity over all my actions, what is it, with all its wondrous faculties--sense, imagination, reason, will--those powers of my being? What is that change which passes upon me, which men call sleep, and that more mysterious and fearful change that must soon pass upon me, and that men call death? How is it that events of former years come back to mind, with all the freshness and reality of passing scenes? What is that principle of my nature that ever assumes to itself the right of command, saying to all my inclinations and passions, thou shalt, and thou shalt not, and when I disobey that mandate, filling my whole soul with misery, my whole future existence with remorse? And what and whence that word _ought_, that has so much to do with me and my pursuits: ought what, and why ought, and to whom?--Am I free, or am I subject to inevitable necessity; if free, then how are all my actions controlled, and predetermined by a divine Providence? If not free, then how am I responsible? Who shall solve this problem; who shall read me this strange inexplicable riddle of human life? Such are the questions and themes which mental philosophy discusses, and we perceive at a glance their intimate connection with the highest interests and personal wants of man as an individual.