It is not a result of scientific study, but merely a freak of philosophy on the part of Schleiden to deny the reality and truth of light phenomena, to call them fantasmagoria created by the free play of the mind. His superstitious belief in philosophical speculation misleads him into abandoning the scientific method of induction and speaking of "waves rushing through ether in restless succession at the rate of 160,000 miles per hour" as being the real and true nature of light and color, in contradistinction to the color phenomena of light. The perversion of this mode of procedure becomes evident by his referring to the material world of the eyes as a "creation of the mind" and to the undulations of the ether, revealed by the "sharp intellect of the greatest thinkers" as "physical nature." The truth of science maintains the same relation to the sense perception that the general does to the special. Waves of light, the so-called truth of light and color, represent the "true" nature of light only in so far as they represent what is common to all light phenomena, whether they are white, yellow, blue, or any other color. The world of the mind, or of science finds its raw material, its premise, its proof, its beginning, and its boundary in sense perception. When we have learned that the nature, or the truth, of things is not back of their phenomena, but can be perceived only by the help of phenomena, and that it does not exist "in itself," but only in connection with the faculty of understanding, that the nature is separated from the phenomena only by thought; and when we see on the other hand, that the faculty of understanding does not derive conceptions out of itself, but only out of their relations with some phenomenon; then this discussion of the "nature of things" is an evidence that the nature of the faculty of thought is a conception which we have obtained from its sense manifestations. To understand that the faculty of thought, although universal in the choice of its objects, is nevertheless limited in that it requires some object; to recognize that the true thought process, that is to say the thought with a scientific result, differs from unscientific thinking by consciously attaching itself to some external object; to realize that truth, or universality, is not perceived "in itself," but can be perceived only by means of some given object; this frequently varied statement reveals the nature of the faculty of thought. This statement re-appears at the end of every chapter, because all special truths, all special chapters, serve only to demonstrate the general chapter of universal truth. FOOTNOTE: [1] E. g., this all-embracing physics.--EDITOR. IV THE PRACTICE OF REASON IN PHYSICAL SCIENCE