and alertness. At home as well as at school, children should be taught to think the thoughts that are suited to their age and capacity; and the neglect of such thought as is quite within their powers should be treated as a fault. We are confident that when a general effort comes to be made for the specific purpose of awakening intelligence, and when, for the furtherance of this end, we throw away a great quantity of the useless lumber with which we now encumber the minds of the young, the result will be a great development of good sense and practical efficiency.
A Text-Book of General Astronomy for Colleges and Scientific Schools. By Charles A. Young, Ph.D., LL.D. Boston: Ginn & Co., 1888. Pp. 650. Price, 12.40.
Prof. C. A. Young's "Text-Book of General Astronomy for Colleges and Scientific Schools" is a work worthy of the reputation of its author, and creditable to the progress of American science. Not only his long experience as a teacher is manifested in the book, but also the character of his teaching, which is clearly that of a man in close sympathy with his students, who perceives accurately the attitude of their minds toward the subject, and knows just when and where to lend assistance. It is no mere compilation, but, to an uncommon extent, an original work. In some text-books of astronomy many things that the really earnest student wants to know seem to have been carefully excluded; he gets results, but not the methods of attaining them, and he can not help feeling that the author has kept him out of the secret, as if it were a performance in prestidigitation. Prof. Young's book is admirably free from this fault. He not only explains principles and methods with unusual distinctness, but he is careful to show the student where to go for further or fuller information. And when he sends the beginner to higher works he starts him off with a clear conception of what he is to go for, which in itself is half the battle. Moreover, he takes pains to point out the limitations of the science—a thing of greater importance than may at first sight appear. For instance, what he says of the nature of the attraction of gravitation is something that the ordinary student rarely gets, but that is of the first importance for a proper comprehension of the subject: "We must not imagine the word 'attract' to mean too much. It merely states the fact that there is a tendency for the bodies to move toward each other, without including or implying any explanation of the fact. So far no explanation has appeared which is less difficult to comprehend than the fact itself. Whether bodies are drawn together by some outside action, or pushed together, or whether they themselves can act across space with mathematical intelligence—in what way it is that 'attraction' comes about is still unknown—apparently as inscrutable as the very nature and constitution of an atom of matter itself; it is simply a fundamental fact" (p. 109).
The whole tone of the book is stimulating and suggestive. It is interesting to the general reader as well as to the student. The chapter on "The Earth as an Astronomical Body," for instance, is a beautiful example of comprehensive treatment combined with clear and succinct statement, including, with an explanation of just those principles that the student needs to have made plain, a summary of the latest knowledge which interests everybody. To particularize a little, we have not seen in any work of the kind so perspicuous and satisfactory an account of the Foucault experiments with the pendulum and the gyroscope as that given by Prof. Young.
Among the little things, which are too often entirely overlooked by writers of text-books, but whose suggestiveness and value in awakening the interest of the student, and clarifying his ideas, have been recognized in this book, we note the demonstration of the eastward deviation of falling bodies (p. 94); the explanation of how the height of the mountains of the moon is measured (p. 170); the ingenious proof of the moon's rotation (p. 154); and the stimulating little example on page 123, showing how the eccentricity of the earth's orbit may be found from the greatest and least apparent diameters of the sun.
As was to be expected from the author's wide reputation and recognized authority as