Page:Popular Science Monthly Volume 33.djvu/430

416 follow, and the causes leading to their foundation clearer." The first of the three divisons of the treatise deals with the characteristics of the chemical atoms. The author begins by stating briefly the necessity for holding the atomic theory, and for a knowledge of the atomic weights, and proceeds to discuss the determination of these weights from vapor-densities, from the specific heat of solids, and by means of isomorphism. He then takes up the relations between the properties of elements and their atomic weights, which have led to the grouping known as Mendelejeff's classification. The second part of the work is devoted to the statistics of the atoms, and in this division are discussed forms of combination of the atoms, the law of atomic linking, and valency. In the third division is treated the dynamics of the atoms, or the doctrine of chemical change. Separate chapters of this section are devoted to chemical change produced by mechanical disturbance and by the action of light, to heat and electricity as causes and as effects of chemical change, to the influence of mass in chemical action, and to the stability of chemical compounds. The author considers that the influence of mass has been too little regarded by chemists, but that its importance is being more and more recognized. He expects great progress soon to be made in the direction of chemical mechanics, pointed out by Berthollet at the beginning of this century. Throughout the volume he shows much solicitude that theories shall be recognized as valuable aids to chemical research, but shall not be formed too hastily, nor trusted too implicitly.

comprehensive treatise is described on the title page as a manual of comparative anatomy, with descriptions of selected types; and the distinctive character of the book, as the late Prof. Rolleston wrote in his preface to the first edition, seventeen years ago, "consists in its attempting so to combine the concrete facts of zoötomy with the outlines of systematic classification as to enable the student to put them for himself into their natural relations of foundation and superstructure." The present edition of the work was begun by the author in 1879, the rewriting of several portions being Intrusted to Prof. Jackson, whom Prof. Rolleston further requested to complete the revision in case he was prevented from doing it himself, and this his death made necessary. The book consists of three sections, the first consisting of descriptions of prepared types, which include the rat and rabbit as types of mammals, the pigeon, ringed snake, frog, perch, and a representative of each of fourteen other classes. The second section comprises descriptions of fourteen plates, four of which are taken from the specimens described in the first part of the work, five others are from specimens of the same animals as described in the first part, but prepared differently, and there are five plates which relate to animals or groups not described before. The remaining two thirds of the volume is devoted to a general account of the animal kingdom, which has a brief classification appended to each class or group, and a bibliography of the most important and recent authorities, which will in most cases give the names of all other accounts worth reading. The two latter features are additions which Prof. Rolleston desired to be made in this edition, and the third chief item of his plan was to enlarge the descriptions of the preparations and accounts of the various classes of animals, and bring them up to the standard of contemporary knowledge. All this has been carried out by Prof. Jackson, though the great length of time which has elapsed since the publication of the first edition has brought with it so many and such vast changes in comparative anatomy that great labor and consequent delay became inevitable.

has had occasion to make extensive studies of the Sunday question and its history, and particularly of the substitution in the Christian Church of the first day for the original Sabbath of the seventh day. The fruits of these studies are partly embodied in polemical works which he baa written in maintenance of the doctrines and practice of the seventh-day Christians; but