Mr. Spencer then proceeds to demonstrate that all science tends to precisely the same great conclusion;--in all directions investigation leads to insoluble mystery. Alike in the external and the internal worlds, the man of science sees himself in the midst of perpetual changes of which he can discover neither the beginning nor the end. If he looks inward, he perceives that both ends of the thread of consciousness are beyond his grasp. If he resolve the appearances, properties, and movements of surrounding things into manifestations of Force in Space and Time, he still finds that Force, Space, and Time pass all understanding. Thus do all lines of argument converge to the same conclusion. Whether we scrutinize internal consciousness or external phenomena, or trace to their root the faiths of mankind, we reach that common ground where all antagonisms disappear--that highest and most abstract of all truths, which is affirmed with equal certainty by both religion and science, and in which may be found their full and final reconciliation. It is perhaps hardly just to Mr. Spencer to state his position upon this grave subject without giving also the accompanying reasoning; but so compressed and symmetrical is his argument that it cannot be put into narrower compass without mutilation. To those interested in the advance of thought in this direction, we may say that the discussion will be found unsurpassed in nobleness of aim, eloquence of statement, philosophic breadth, and depth and power of reasoning. This portion of the work embraces five chapters, as follows: I. Religion and Science; II. Ultimate Religious Ideas; III. Ultimate Scientific Ideas; IV. The Relativity of all Knowledge; V. The Reconciliation. The second and larger portion of _First Principles_ Mr. Spencer designates "The Laws of the Knowable." By these he understands those fundamental and universal principles reached by scientific investigation, which underlie all phenomena, and are necessary to their explanation. Certain great laws have been established which are found equally true in all departments of nature, and these are made the foundation of his philosophy. The sublime idea of the Unity of the Universe, to which science has long been tending, Mr. Spencer has made peculiarly his own. Through the vast diversities of nature he discerns a oneness of order and method, which necessitates but one philosophy of being; the same principles being found to regulate the course of celestial movement, terrestrial changes, and the phenomena of life, mind, and society. These may all be comprehended in a single philosophical scheme, so that each shall throw light upon the other, and the mastery of one help to the comprehension of all.