The primary conceptions of physical and mental science will be given chief consideration. And this will be done with the main purpose of demonstrating that they may now be reduced to a single system of formulated knowledge most serviceable, in common, for all the sciences and for ethics, sociology, and religion. This task presents great difficulties, even in the style of writ ing it demands. It must take all sorts Of readers into different regions of science, and make them familiar with details in ways difficult to most persons, though they seem unnecessarily element ary and tedious to each particular specialist. On the other hand, it must entice each specialist to go outside of his chosen domain and to interest himself in the summarizing of all departments Of knowledge, consistently with one another, in ways he has, perhaps, grown to regard as futile for his particular work. Again, it must persuade the religious enthusiast that the path to be pursued is that in which his ardor may be most devoutly directed. From the outset, therefore, the author begs of all parties a serious patience worthy Of the problem and of its fruits. Such a work demands an introductory outline of the fields to be covered, of their present aspect, and Of the reasons requiring the reconsideration of them here proposed. N O philosophic thought is more hackneyed than that the uni verse is one and indivisible. As yet, however, it is a mere faith. NO system has yet gathered all the Spheres of learning under it in actual detail. On the contrary, the most striking feature Of the present map of the world's wisdom is that it still displays the two chief bodies of human knowledge in Open dis junction; in as distant and inhospitable relations as were the Eastern and Western Continents before the voyage of Columbus. I refer to the intellectual hemispheres of mental and of physical science. Some of the main hypotheses, upon which the business Of each now proceeds, are notoriously contradicted by the most substantial conclusions of the other. For example, the entire bulk of the physical sciences is conducted on the assumption that its world is spatial in ways that make that word inapplicable to the human mind; 1 while at the same time there is little like lihood, now, of finding a competent psychologist who does not incline to the belief that matter and mind are ultimately of one sort. Nor are there lacking other examples equally striking and more pertinent to the world's welfare and daily life. It is to these confusing and harmful antagonisms, constituting the classic strife between philosophy and science, idealism and realism, spirit and matter, since the beginning Of history, that this Treatise will bring peace.