Page:Popular Science Monthly Volume 60.djvu/482

474 have walked the face of the earth, but | existing whales are the greatest of animals, and the living elephants are larger than the mastodon and compare favorably with the mammoth. The first of the dozen chapters treats of fossils and how they are formed, while the; last discusses the problem why do animals become extinct, suggesting some of the causes which lead to extermination, and showing that in some in-I stances apparent extinction is in reality evolution, one species passing into another, so that the race endures while individuals die out; this is well illustrated by the chapter devoted to the ancestry of the horse. Reading the riddles of the rocks tells how animals are interpreted by their fossil remains even if it is not possible to reconstruct an animal from a single bone or tell its size and habits from a tooth. Other chapters are devoted to birds of old, the dinosaurs, feathered giants, the mammoth and the mastodon, and at the end of each chapter is stated where the best examples of the animals described may be seen, while in many instances the size of the largest specimens is given. The book is illustrated with restorations of extinct animals drawn by Mr. C. R. Knight and J. M. Gleeson, and while these may look a little tame beside some of those that have appeared in the Sunday papers, they are the result of long and careful study and may be regarded as among the most accurate that have been made.

A by Philetus H. Philbrick (Wiley and Sons), treats only of the surveying work of railroad location and construction, but this is set forth in a thorough and interesting manner. No logarithmic tables are given, as is usual in such field-books, the author claiming that 'they are but little used and should not be used at all.' Whatever may be thought of this remarkable statement, it must be said that the twelve pages given on approximate and abridged methods of numerical computations are of great interest and value; if such methods were generally taught to engineering students it would certainly prove highly advantageous in enabling them to perform computations with a degree of precision consistent with the given data.

by James H. Fuertes (Wiley and Sons), treats this important topic mainly from the engineering point of view. Both slow filtration by sand beds and rapid filtration by mechanical means with the help of a coagulent are fully described, the methods of clearing and operating being in particular well exemplified by illustrations of the details of plants recently installed. The purification of river waters carrying much suspended matter is discussed in connection with the results of the experiments made at Pittsburgh, Cincinnati and Louisville. For towns where it is doubtful whether a sand filter bed need be covered the author suggests that a combination of the slow and rapid filtering methods might be made, the former being used in summer and the latter in winter. The book bears evidence of having been prepared with care, and it is a valuable addition to the literature of a subject which constantly increases in importance as the public comes more and more to realize that the use of pure water diminishes the death rate from zymotic diseases.