The point of present importance in the use of these discriminations is to make clear to the mind of the reader what perhaps is sufficiently implied in the very terms themselves, namely: that _Impression_ and _Expression_ are correlative to, and, in a sense, exactly reflect each other; that the totality of _Impression_, or the Universe which enters the mind through the senses, is repeated--with a modification, it is true, but still with traceable identity, or with a definite and unbroken relationship--in the totality of _Expression_, or in the Universe of Art, taken as the entirety of what man does or creates. It is by the mediation of Science or Knowledge, that one of these worlds is converted into the other. Nature or _Impression_ is the aggregate of the Rays of Incidence falling upon a mirror; Science is the Reflecting Mirror; and Art or Human Performance is the aggregate of the Reflected Rays, whose angles can be exactly calculated by the knowledge of the angle of incidence. Science or Knowledge is not only the mirror which makes the Reflection, but it is the plane or level which is to furnish us the means of adjusting the angles; of knowing their correspondence or relation to each other; and of translating the one into the other. Science must, therefore, as it develops, be the instrument of informing us of the exact analogy between Nature and Art; and must enable us so to apply the Laws of Nature, or the Laws of God as exhibited in Nature, that they shall become a perfect canon of life and action, in all our attempted performances and constructions, whatsoever they may be; or, _vice versa_, it must enable us from the knowledge of the laws of our own actions to reveal the secrets of Nature, and to know, by the analogy, in what manner she acts. It will then perhaps be found that the Moral Code, as dictated by inspiration, is only the forecast, through that method, of what is destined to be more perfectly revealed to the intellect, when the veil is rent by the millennial perfection of man. It will be perceived by the reader that the term Art is here employed in a larger than its usual sense, although the analogy in question has a special intensification when we confine the term to mean, as it ordinarily does, the _choicest performances_ of man. The term Science has also a larger and a smaller extension. In the larger sense it means the totality of knowledge _extracted from Impression_ or the observation of Nature, and distinguished _from mere Impression_ or Nature on the one hand, and from _Expression_, Action, Performance, or Art--the reprojection of the knowledge into new forms of being--on the other hand. In the more restricted sense, Science means systematized knowledge, or, still more specifically, the Body of Principles or Laws in accordance with which knowledge becomes systematized in the mind.