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132 leaf can not be profitably studied without a knowledge of its structure and functions; and it is also important to know what is the systematic position of each of the various plants whose leaves afford the material for study. In a word, the student should not attempt to read the book straight through from the beginning as if it were a novel. On the contrary, he may begin with any one of the four parts as his main subject; but that part must be studied in close relation with the other three parts"; and this method of proceeding is facilitated by the insertion of a large number of cross-references in the text.

A satisfactory account is given by C. Francis Jenkins in Animated Pictures of the development and present state of chronophotography, or the art of "conveying by persistence of vision a counterfeit impression of objects in motion through the display in rapid succession of a series of related pictures." The story shows very clearly that this, like most other inventions of consequence, is no sudden discovery, but is the culmination of a very long series of experiments. The principle of it is embodied in the toy, the zoetrope, the origin of which is not known, though a citation from Lucretius indicates that something of the kind existed in his time. With the discovery of instantaneous photography, a new application of the principle of the zoetrope was found. Muybridge and Marey were pioneers in this development with their photographs of the motions of animals valuable in sciences. Since their work was begun the photographic processes and apparatus have been greatly improved. Mr. Jenkins forecasts a brilliant and useful future for the art, which he hopes will be prosecuted along the line of other than its present most popular uses. The book is practical as well as historical and prophetic, and contains an account of Mr. Jenkins's phantoscope as the first successful "moving picture projecting apparatus," for which he received the Elliott Cresson medal from the Franklin Institute.

The Metric System of Weights and Measures, prepared by Mr. A. D. Risteen, and published by the Hartford Steam-Boiler Inspection Company, Hartford, Connecticut (price, $1.25), gives what has long been wanted—a neat volume, convenient for the pocket and durably bound, furnishing tables for instantly converting all the metrical units up to one hundred of each into those of the English weights and measures, and vice versa. Calculation, being needed only for the numbers above one hundred, for which there are already short devices, is reduced to the lowest possible limit.

Terrestrial Magnetism, an international quarterly journal, edited by L. A. Bauer and Thomas French, Jr., and published at the University of Cincinnati, is the recognized organ of the International Conference on Terrestrial Magnetism and Atmospheric Electricity. The September number, 1898, contains the proceedings of the conference, which met in connection with the last Bristol meeting of the British Association. It contains in full the welcoming address of Prof. W. E. Ayrton, the opening address of A. W. Rücker, president of the conference, and ten of the papers read at the meeting.

The name of Prof. John Trowbridge as author of such a book as Philip's Experiments; or, Physical Science at Home (D. Appleton and Company, $1) is a sure guarantee of its scientific value. The author has given a chapter substantially out of his own experience, for he says his taste for science and for drawing were stimulated by his father in the manner here described. His object in publishing it is "to show that a few moments devoted each day at home to simple investigations can result in habits of self-reliance in the acquirement of a modern language and in the study of the art of drawing." He endeavors also to show how to cultivate a taste for mathematics by studying practical problems in surveying and in sailing a boat; and how much a parent can accomplish in the formation of a son's tastes without special knowledge, and without the expenditure of much time and money.