# Popular Science Monthly/Volume 60/March 1902/Scientific Literature

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POPULAR BOOKS ON EXTINCT ANIMALS.
If 'Dragons of the Air,' by H. G. Seeley, is not in quite so popular a vein as its title might indicate it is none the less a clear, comprehensive and interesting account of that remarkable group of reptiles, begging Professor Seeley's pardon, known to science as pterodactyls. No one is better qualified than Professor Seeley to write of them, as his acquaintance with these flying dragons is of many years standing, and he has made them the objects of special study. He tells us that he has attempted to show how a naturalist does his work and illustrates the methods of the paleontologist by briefly comparing the various parts of existing flying creatures with one another and applying the information thus gained to the study of the skeleton of the pterodactyls. Part by part the various portions of this skeleton are passed in review, and we are told the more important variations found in the widely varying members of the group and between them and other flying animals. Then, after a chapter devoted to evidences of animals' habits, from which the reader may learn how the conclusions regarding the food, covering and flight of pterodactyls have been reached, we are introduced to the various species that have existed at different periods of the earth's history. In connection with this are given some restorations of the more remarkable of the dragons of the air, including the extraordinary Dimorphodon with a head bigger than its body. Accompanying these restorations are plates showing the specimens on which they are based, and the skeletons built up from these specimens. Most of the figures represent the animals as running on all fours, an attitude that is questioned by some of our paleontologists, notably by Dr. Williston, who considers that they walked on the hind legs alone and that the great Ornithostoma in particular could not possibly have used its fore limbs as legs. The concluding chapters contain a discussion of the relations and origin of the pterodactyls and, from what has been said in other parts of the book, we are in a measure prepared to find that Professor Seeley advocates a closer affinity between birds and pterodactyls than is usually accorded them. Most anatomists will probably agreee in considering that many features of the skeleton of pterodactyls, such for example as its remarkable pneumaticity are due to modifications for flight, but the author considers that Pterodactyls and Birds form two parallel groups which may be regarded as ancient divergent forks of the same branch of animal life. But whether we accept all Professor Seeley's deductions or not we may safely accept his facts and we are indebted to him for having placed so much information within our reach and for having given it in so readable a form.
'Animals of the Past,' by Frederic A. Lucas, is more popular in its line than 'Dragons of the Air,' and wider in its scope, dealing with a number of the more striking or more interesting of extinct animals and especially with those of gigantic size. Here, however, Mr. Lucas's mission in life appears to be to correct the widespread impression that the animals of the past were so very much larger than those of the present. Some of the dinosaurs we are told were the largest animals that ​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.
ENGINEERING.
A 'Field Manual for Engineers' 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.
'Water Filtration Works,' 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.