man of science to be the more marvellous in their attributes the more they are investigated, and are also proved to be in their ultimate natures absolutely incomprehensible--as absolutely incomprehensible as sensation, or the conscious something which perceives it--whoever clearly recognises this truth, will see that the course proposed does not imply a degradation of the so-called higher, but an elevation of the so-called lower. Perceiving, as he will, that the Materialist and Spiritualist controversy is a mere war of words,--in which the disputants are equally absurd, each thinking that he understands that which it is impossible for any man to understand,--he will perceive how utterly groundless is the fear referred to. Being fully convinced that no matter what nomenclature is used, the ultimate mystery must remain the same, he will be as ready to formulate all phenomena in terms of Matter, Motion, and Force, as in any other terms; and will rather indeed anticipate, that only in a doctrine which recognises the Unknown Cause as co-extensive with all orders of phenomena, can there be a consistent Religion, or a consistent Philosophy." This is clear enough; yet such is the crass density of some objectors that eighteen years after the above was written, Mr. Spencer, in answering criticisms on First Principles, had to rebut the charge that he believed matter to consist of "space-occupying units, having shape and measurement." The Principles of Psychology was both preceded and followed by a series of essays in which the process of change from the "homogeneous to the heterogeneous," i. e., from the seeming like to the actual unlike, was expounded. Mr. Spencer tells us that in 1852 he first became acquainted with Von Baer's Law of Development, or the changes undergone in each living thing, from the general to the special, during its advance from the embryonic to the fully-formed state. That law confirmed the prevision indicated in the passages quoted above from Social Statics, and impressed him as one of the three doctrines which are indispensable elements of the general theory of Evolution. The other two are the Correlation of the Physical Forces, or the transformation of different modes of motion into other modes of motion, as of heat or light into electricity, and so forth, in Proteus-like fashion; and the Conservation of Energy, or the indestructibility of matter and motion, whatever changes or transformations these may undergo. In permitting the quotation of the useful abstract of the Synthetic Philosophy which, originally drawn up for the late Professor Youmans, was imbodied in a letter to the Athenæum of 22d of July, 1882, Mr. Spencer was good enough to volunteer the following details to the writer:-- "You are probably aware that the conception set forth in that abstract was reached by slow steps during many years. These steps occurred as follows:--