Page:Popular Science Monthly Volume 42.djvu/579

Rh value from the practical point of view, while the scientific aspect of the subject can not fail to interest and stimulate the intelligent reader.

of the most obvious and radical changes wrought by modern investigation in the science of physics is the greater importance which the phenomena of energy have assumed. Until comparatively recent times matter was considered the far more essential factor, and received a considerably larger share of attention. The reverse is now the case, and, as Prof. Barker well says, "The physics of to-day is distinctively the science of energy. Henceforth every physical change must be regarded as conditioned upon the transference or the transformation of energy. Hence, the classification which has been adopted in the present work is based on the most recent views of energy, considered as being ultimately a phenomenon of the ether."

The introductory portion of this book deals with the general physical relations and the laws of motion. Energy is next treated of as a mass condition, and work as the transference or transformation of energy. Potential is considered as a consequence of mass attraction. Matter is then treated of with reference to the modern views of its structure. Heat comes next, under the head of molecular physics. The remainder of the work is devoted to the phenomena of the ether, which are classified as follows: ether vibration or radiation; ether stress or electrostatics; ether vortices or magnetism; and ether flow or electrokinetics. The metric system is used throughout. What illustrations there are are well placed, but they are not as numerous as might be wished. There is a detailed table of contents, and a useful index.

The book is not, like many scientific works, an encyclopædia, nor is it, as some of the others are, a purely theoretical treatise. It combines very happily the important experimental facts of the science with the more probable theory or theories based upon their consideration. It fully justifies Prof. Barker's reputation as a thorough scientist. It is written in a plain and lucid style, and is very readable. The author's treatment of the subject varies somewhat from that of the old standards, but it is a treatment which recent work has been increasingly leading up to, and, in fact, making necessary.

The old text-books, notwithstanding frequent revisions, are unsatisfactory, and a new book, not only embodying the results of the most recent investigations, but also applying these results in the treatment of the subject as a whole, has been a growing necessity. Prof. Barker has given us just such a book, and it is fortunate that so careful and thoroughly equipped an author was at hand.

one who wishes to have a handsome volume, fully illustrated, and giving a remarkably interesting account of the discoveries that have been made in regard to the peoples that lived before any mode of writing was invented, should get this work of De Nadaillac. The author begins with a general sketch of the stone age, in which he shows that its duration and its place in time can not be set off by any hard-and-fast bounds. He then proceeds to tell what has been learned as to the food of early man, which involves the subjects of prehistoric hunting, fishing, and cannibalism. The author names the horse, the aurochs, the stag, the reindeer, and other animals as furnishing food for the ancient men of Europe, and he names place after place where human bones, charred, and all those containing marrow broken, just as the bones of the lower animals were treated, give evidence of cannibalism. In rapid succession he touches upon the numerousness of animals in the stone age, the weapons used by man in killing them, the implements used in fishing, and various early efforts at navigation. Taking up weapons, pottery, and other articles of use or ornament more in detail, he describes implements from the caves of France, the river valleys of America, and from England, Italy, Spain, Algeria, and Hindostan. He speaks of pottery from Germany, Italy, France, Belgium, and other countries. This leads to a few words on the ancient use of fire, after which come descriptions of