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Rh elements and their compounds present themselves as a periodic function of their atomic weights.

Attention must also be directed to another feature of this book, as important as it is novel in a text-book on inorganic chemistry. When bodies enter into chemical combination, heat is almost invariably evolved; and, on the other hand, when a compound is decomposed into its constituents, heat is absorbed and transformed into chemical energy. The study of these phenomena, thermo-chemistry, is here introduced in connection with the different groups of the elements, thus familiarizing the student from the start with one of the fundamental principles of chemical science, yet one which has heretofore been almost entirely relegated to works on theoretical chemistry. In short, Von Richter offers a most clear, vivid, and interesting presentation of his subject.

Ventilation of Buildings.—This essay was originally prepared for delivery before an audience, which will account for the fact that it contains remarks and comments on subjects which can hardly be considered as specially connected with the ventilation of buildings, though in themselves of interest and importance. It was written for English conditions, and the present copy has been re-edited and enlarged by Mr. Greenleaf to adapt it for use in this country. The needs for ventilation are first discussed, and then a method is given for ventilating private houses, showing how this method may be adapted to old and to new buildings. Appended to the book is a reprint from "Van Nostrand's Magazine" on "How much Ventilation?" by the editor of this issue.

Water-Meters.—A brief treatise on some of the principal forms of water-meters in

use, embracing descriptions of the prominent features of two forms of piston-meter, the Worthington and the Kennedy, and three forms of velocity-meters, the Siemens of English manufacture, the Siemens of German manufacture, and the Hesse meter. A series of tests conducted with the latter is given. An appendix contains a translation of an article on some forms of water-meters not considered in the text previous. This article is by Charles Andre and was published in the "Genie Civil." The book is intended mainly for hydraulic engineers.

The Preservation of Timber by the Use of Antiseptics.—A paper prepared for the Institution of Civil Engineers and discussed before them; the discussion is appended. It is a careful review of the history of preserving timber, and the chief methods adapted to that end.

Mechanical Integrators.—Descriptions of various devices that may be designated as mechanical aids to mathematical computation; chiefly such are considered as will prove of value to engineers.

text-book intended in the first place for students fitting for examinations at English colleges. Valuable hints are given as to the preliminary analysis, then follow schemes of examination for bases and for acids, and appended are notes on apparatus, on the preparation of reagents, etc. A quite extensive list of the chemical symbols of substances made use of in the analytical work is given. These symbols are arranged in alphabetical order, and, as the corresponding names are also given, will prove very convenient for the student.

presentation, in the form of conversations, of the elementary conceptions of philosophy. This book is intended to serve as an introduction to metaphysics and logic. It is essentially based on the writings of S. H. Hodgson, principally on "Time and Space," by this author.