Page:Popular Science Monthly Volume 30.djvu/585

Rh small a volume seems quite formidable, but each takes up a special part of the subject and treats of that.

Mr. Wells discusses the simple outfit needed by beginners in the fascinating study of microscopy, gives suggestions as to proper objects to be studied and their preparation, and tells of some simple experiments that will entertain the young student at home in the winter-time, when snow and storms forbid the seeking of subjects for his study in field and meadow.

Mary Treat tells of some interesting plants and animals whose life-history she has observed and studied under her microscope; and Mr. Sargent's contribution is on "A Home-made Microscope, and how to use it," an article which will be sure to please boys of an inventive turn of mind. Quite a number of illustrations are given, which add considerably to the interest and value of this little treatise.

properties of the luminiferous æther appear to have been accurately determined, except that of transmiting light at the rate of 186,300 miles per second, and the ability to convey a definite amount of heat energy from the sun to the earth.

Proceeding from these data, the author of the first book on our list seeks, by a long train of reasoning and considerable figuring, to determine and establish what certain other properties this æther must possess. He comes to the conclusion that its density must be such "that a volume of it, equal to about twenty volumes of the earth, would weigh one pound," that the tension is such "that the pressure on a square mile would be about one pound," and that the specific heat is such "that it would require as much heat to raise the temperature of one pound one degree Fahrenheit as it would to raise about 2,300,000,000 tons of water the same amount.

In the "Addenda" are given extracts from Newton's "Principia," and from the works of Clerk-Maxwell bearing on kindred themes.

The "Hand-Book of Mineralogy" is intended by the author as an aid in determining the minerals found in the United States. It gives briefly the prominent and distinguishing characteristics of the different minerals, and aims at presenting the classifications usually adopted in arranging cabinets,

After a few introductory remarks on the apparatus and reagents needed, and a short chapter on blow-pipe reaction, follows the part devoted to the determination of species. This comprises two tables, the first for the "preliminary examination," the other for the "final examination," by means of which tables the nature of a specimen may be readily and rapidly determined.

The remaining part of the work is given to a description of the species, to the chemical classification, and to a classification by basic elements and ores.

A copious system of cross-references is supplied.

The "Flow of Water in Open Channels" is a book of formulæ and tables designed to save time and work for hydraulic engineers who make use of the formulæ of D'Arcy, Kutter, and Bazin, in preference to the older formulæ. As the former, however, although more accurate, arc also as a rule more complicated and more troublesome in their application, a book of this kind, practically a ready method of applying the new formulæ, will probably render the use of them more general and popular.

Two objects are intended to be accomplished by the treatise on the construction of helicoidal oblique arches. In the first place, a clear and concise treatment of the construction is aimed at; and in the second place it is attempted to make plain and simple all problems connected with the theory or construction. The author believes that a thorough understanding of the process of the generation of helicoidal surfaces will remove all difficulties that usually present