Since M. Mouret is manifestly an earnest student of the topic of relation-lore this language shows that he has at best only a second or third-hand knowledge of what DeMorgan and Boole really did. He ought to have known that in the recondite field of research in question all really competent treatment of the same would be very far from having any “popular” quality. For a man to discourse of relation-lore in ignorance of what DeMorgan, the very father of the “Logic of Relatives,” accomplished is like discoursing of Darwinism in ignorance of “The Origin of Species.” We opine that when M. Mouret shall have consulted the great memoir of DeMorgan in the tenth volume of the “Cambridge Philosophical Transactions” or better, when he shall have become acquainted with the more developed work of Mr. C. S. Peirce, to whom beyond question relation-lore is most indebted for its present state of progress, he will have a better esteem for the value of the “tentatives” of DeMorgan and Boole and their disciples. Mr. Peirce has published three principal papers on the subject in question. The first of these was published in 1870 in the ninth volume of the “Memoirs of the American Academy of Arts and Sciences.” Then in 1880 and in 1884, while Mr. Peirce was lecturer on logic at Johns Hopkins University, he published in the _American Journal of Mathematics_ two papers dealing more or less extensively with relation-lore. One of these his “_Hauptwerk_” as it is called by Professor Schroeder of Carlsruhe, appears in the third volume of the journal mentioned and the other in the seventh volume of the same. Mr. Peirce was one of the contributors to our new American “Century Dictionary,” and in that work under the definitions of Relation and Relativity there appears a summary treatment of the subject which is as we take it the work of Mr. Peirce and which might have given to M. Mouret hints which he would have appreciated. Also the editor of this magazine in his article “Are there Things in Themselves?” in the January 1892 number thereof incidentally touches upon the topic under consideration in such a way as to correct some of the more inveterate misconceptions. IV. M. MOURET’S THEORY OF RELATIONS. The article of M. Mouret is in so many points so excellent a discourse that the chief reflection one is inclined to make is that upon its own principles it ought to have been better. He seems to have been widely awake to the primordial nature of relations as philosophical data. He says: “Every notion or relation is a _function_ of relations more directly known and enters as a relational element into other relations less proximate to the common sources,” and also that “every concept or notion ought to resolve into a group of relations.”