148 



NA TURE 



[December 15, 1892 



A careful perusal will show that the author considers 

 it desirable that all matters pertaining to units, defini- 

 tions, symbols, &c., should be carefully attended to. 

 But in his treatment of these he has not been entirely 

 successful. 



Take, for instance, his definition of the moment of a 

 force on p. 15 :— " The moment of a force is equal to the 

 force multiplied by the perpendicular distance from a 

 point on its line of action." This is rather ambiguous, 

 and we should prefer to see the words, with respect to 

 a point, included in the definition. 



In a footnote,'p. 214, objection is taken to/ being used 

 for acceleration, since it "naturally represents a force.'' 



/ 



Then why use e for strain in the formula e 



where 



e just as naturally represents an elongation, and strain 

 is not an elongation, as the author clearly shows in 

 another footnote on p. 232 ? 



W 

 Again, in a footnote on p. 2 we have : " M = ' 



g 

 where M stands for the mass, W for the weight in pounds, 

 and g for the acceleration of gravity." 

 Now on p. 215 the reader is asked to accept as correct 



the formula for centrifugal force, P = lbs., but 



W M7/2 



(continues the author) since M = — , then P — — ;- 



poundals. Why should this substitution produce the 



change from pounds to poundals ? We fail to see what 



is gained by having an ellipse for the figure representing 



motion in a circle. 



There is a want of consistency when an acceleration 



is spoken of as " a feet per sec. in one second " in 



one place, and as " <? feet per sec." on p. 219. On 



Wt/- 

 the same page, too, -— - should evidently be read as 



Wt/-' 



2^ ' 



The examples worked out in the chapter on bending 

 moments will show the student how to apply the prin- 

 ciple of moments to the case of a beam loaded in any 

 given manner. This is preferable to merely using a 

 set of formula, a system attended with most disastrous 

 results. 



At the end of each chapter will be found a good 

 selection of examples on the matter considered therein. 

 We are informed that another volume dealing with the 

 more advanced portions of the subject is in the course 

 of preparation. G. A. B. 



OUR BOOK SHELF. 



Man and the Glacial Period. By G. Frederick Wright, 

 D.D., LL.D., F.G.S.A. (London : Kegan Paul, 

 Trench, Triibner and Co., 1892.) 

 The title of this book raises expectations which the con- 

 tents fail to satisfy. Out of 374 pages only sixty are 

 devoted to the consideration of " the relics of man in the 

 Glacial Period," and the treatment of the subject is, to 

 say the least, uncritical. The reader does not learn from 

 Prof. Wright that strong doubt has been expressed as to 

 whether some of the " finds " of human relics in North 

 America were really made in undisturbed glacial deposits, 

 while his discussion of the European evidence is crude 

 NO. 1207, VOL. 47] 



and inadequate, not to say misleading. The author ha* 

 apparently only a slight acquaintance with the literature 

 of the subject, acquired chiefly from such recondite 

 sources as Lyell's "Antiquity of Man," and treatises on 

 general geology. Of the many interesting facts bearing 

 on man's relation to the Ice Age which have been dis- 

 covered since those works were published our author is ap- 

 parently ignorant. Nor has" a summer spent in Europe '' 

 sufficed, as who could expect that it should, to make up 

 for his other deficiencies. Fortunately, the major portion 

 of his volume deals with the glacial phenomena of North 

 America, for here he is on safer ground. We feel sure, 

 however, that many of his statements and conclusions 

 will receive scant support from geologists across the 

 water. It would be interesting to know, for example, 

 what evidence can be adduced to show that the southern 

 part of the United States was submerged during the 

 Glacial Period to the extent of 500 feet, so as to bring 

 the waters of the Gulf of Mexico into Illinois and 

 Indiana. Again, we were under the impression that the 

 author's " Ohio Lake," which he supposes came into 

 existence when the great ice-sheet advanced into that 

 region, had been effectually disposed of by Mr. Leverett 

 and Prof. Chamberlin. Throughout the book the unity 

 of the glacial period is confidently upheld, a view which 

 Prof. Wright is, of course, entitled to maintain ; but he 

 might have informed his readers that with few exceptions 

 American geologists are quite of another opinion. He 

 fails to understand the evidence adduced by Chamberlin 

 and others in favour of the periodicity of glaciation, while 

 so far as one can gather from his pages, he seems to 

 know nothing of the facts bearing on this question which 

 geologists in Europe have accumulated, especially during 

 the past few years. 



Altogether we much prefer the author's earlier work, 

 " The Ice Age in North America," of which the present 

 is more or less of an abstract. In the former the facts of 

 American glacial geology were given in considerable 

 detail, and the writer's crude speculations and hypotheses 

 were less obtrusive. Should the present work come to a 

 second edition we would advise Dr. Wright to get some 

 scientific friend to assist him in its revision. Loose un- 

 scientific phraseology and incorrect definitions are of not 

 infrequent occurrence throughout the volume. Thus we 

 read of " glacial ice," of " beautiful crystals of porphyry," 

 &c., and are told that neve is the "motionless part " of 

 a glacier, although a little further on we learn that it is 

 from this " motionless " ndvd that " the glacier gets both 

 its supply of ice and the impulse which gives it its first 

 motion." Obviously Dr. Wright is unacquainted with the 

 observations of MM. Pfaff, Kloche, and Koch on the 

 movement of ndve, while he might increase his knowledge 

 of glacier motion by studying what Messrs. McConnel 

 and Kidd have to say upon that interesting subject. 



Beetles, Butterflies, Moths, and other Insects. By A. W. 



Kapple and W. Egmont Kirby. (London : Cassell 



and Co., 1892.) 

 This work is a slight sketch of the more prominent 

 British insects, intended for youthful and very inex- 

 perienced entomologists. The first section is devoted 

 to classification, the key to the orders of insects being a 

 fairly workable one, though it takes no account of the 

 very numerous exceptions. Then follows a section on 

 structure, in which when describing the eye the authors 

 ignore the latest experiments on the subject, proving that 

 the compound eyes form but a single image of the object 

 seen ; they also treat the tongue or proboscis as if it were 

 homologous throughout the orders, whilst in lepidoptera 

 it is developed from entirely different organs from what it is 

 in the others, except in the very lowest family ; and again 

 when describing the legs they fall into the almost 

 incredible error of speaking of the first joint as the 

 trochanter, saying it is joined to the thorax by a hinge- 



