Page:Popular Science Monthly Volume 55.djvu/289

Rh strata for the chronology, and to ascertain as far as he can the conditions existing during the deposition of the several strata or groups of strata. After an account of the growth and progress of stratigraphical geology, the nature of the stratified rocks and the law of superposition are discussed; the test of included organisms and the methods of classification are explained, the evidences of conditions under which strata were formed, and other theoretical points are considered, and the several geological systems or periods are enumerated under the English nomenclature. Finally, the various estimates of geological time and the bases on which they are made are reviewed.

The American Book Company publishes as a part of the Eclectic System of Industrial Drawing an excellent manual of the Elements of Perspective, by Christine Gordon Sullivan, of the Cincinnati public schools. It consists of explicit directions and rules on the general principles of the art, with applications in Isometric Projection and Oblique Perspective, given in concise form and simple, clear language, amply illustrated, and supplemented by problems, in solving which the rules are made practical.

A convenient manual on Gas and Petroleum Engines has been prepared by A. G. Elliott from the French of Henry de Graffigny for Whittaker's Electro-Mechanical Series, in recognition of the interest that has been awakened in the application of such engines to supply the place now occupied by horses in drawing vehicles. One chapter deals exclusively with the theory of the gas engines. Other topics treated of are the history of the gas engine, the description of existing gas engines, carbureted air engines, petroleum engines, gas-generating plants, engines for use with poor gases, and the maintenance of gas and oil engines. (The Macmillan Company, 75 cents.)

Laboratory Exercises in Anatomy and Physiology (New York: Henry Holt & Co., 60 cents) have been prepared by James Edward Peabody for practical application. The precept is emphasized that the pupil should" be led to see that most of the materials required for observation and experiment are furnished by the organs and tissues of his own body. Directions which have been found in the author's experience necessary to guide the pupil in his observations and experiments are given at the beginning of each topic. The questions following them contemplate the student's seeking the facts from the material itself, and he is expected to be trained to distinguish observed results from the inferences that may be drawn from them. Some home study is contemplated, the results to be afterward reported in class. The book consists almost entirely of directions for experiments, and is interlined with blank sheets for recording observations.

Geographical Nature Studies (American Book Company) is intended by the author, Frank Owen Payne, to assist the teacher, and by pointing out the relations, often unrecognized, between familiar phenomena and home geography to guide the study of the class to definite and practical ends. The lessons are intended to fit the comprehension of the youngest pupils, to promote the cultivation of habits of accurate observation, and to stimulate a desire for more knowledge and broader views of the world. They lead directly up to the point where the more formal study of geography from a text-book begins. The lessons may be used as reading exercises and for topical recitations, and exercises are introduced which may assist the cultivation of the power of correct verbal expression in the statement of facts. The exercises concern weather, animals, physical phenomena, and objects about us, and are very various.

Impressions of Medusæ have been observed on the Jurassic lithographic limestones of Solenhofen, and some "problematic fossils" on the Lower Cambrian rocks of Sweden have been regarded as derived from Medusæ. Certain nodules, bearing what looked like flattened-out starfishes—"star-cobbles" they were called—have been found among the fossils of the Coosa Valley, Alabama. Director Charles D. Walcott, of the United States Geological Survey, concluded that these also represented Medusæ, and began an investigation of them which involved a comparison with the Swedish and Bavarian specimens, and was at last enlarged so as to