266 



NA TURE 



[January i8, 1900 



laws of motion is of the nature of definition, and how 

 much is a statement of facts ascertained experimentally, 

 is not disclosed. To assert that these laws still form the 

 simplest foundation for the subject is to ignore the pro- 

 gress that has been made since the publication of Thom- 

 son and Tait's " Natural Philosophy." The difficulties 

 into which writers who follow Newton uncritically must 

 needs fall can be illustrated by sentences on pp. 27 and 

 28. On p. 27 we read, " Force is defined as any cause 

 which alters the momentum of a body " ; and on p. 28 

 we are told that force is " merely another name " for 

 *' the vector-acceleration of momentum." This makes 

 the same word do duty for the cause of the change and 

 the rate of the change. Others of the definitions given 

 are wanting in precision. The definition of the mass of 

 a body as the quantity of matter in it is a definition of 

 one previously undefined thing in terms of another. The 

 description of the first law of motion as a " statement of 

 the inertia of matter " is not helpful ; inertia is a property 

 of matter under ordinary conditions, and the first law is 

 a statement about matter under conditions in which it 

 has never been observed. It ought to be realised that 

 the three laws form a connected system, and that all of 

 them are as much needed as any one of them for the 

 precise definition oijorce, or the exact statement of the 

 in«/tia of matter. The definition given of %vork done is 

 ob'Scure ; the work of a force is defined as a product, and 

 no indication is given of the sense in which this product 

 can be said to be "done." What is wanted here is much 

 the same as in the case of force : we all have an anthro- 

 pomorphic idea that some cause must operate to start 

 or stop the motion of a body ; we have a similar idea 

 that a man has done something when he has lifted a 

 weight or thrown a cricket ball, and these ideas should 

 be taken hold of and made precise by the introduction 

 of measurable quantities which are adequate to represent 

 them. 



The difficult ground of definition and statement of 

 principles once covered, the rest of the book is for the 

 most part excellent, the geometrical methods employed 

 being especially elegant. Room is found for an ele- 

 mentary discussion of strain, of compounded simple har- 

 monic motions, of attractions, including the distribution 

 of electricity on a sphere under influence, and of the 

 velocity of waves along a stretched cord, in addition to 

 interesting and unhackneyed accounts of the matters 

 which are the stock-in-trade of books on the elements of 

 mechanics. The book on the whole is thoughtful, in 

 many parts it is much better than the current text-books, 

 and the parts that call for criticism are no worse than 

 the corresponding parts of most other books on the sub- 

 ject ; but they are the most important parts, and they 

 might have been so much better. There was a great 

 opportunity, and it has been missed. A. E. H. L. 



THE SCIENCE OF LAND FORM. 

 Physical Geography. By Prof. W. M. Davis, assisted by 

 W. H. Snyder. Pp. xvii -f- 428 4- 9 plates. (Boston 

 and London : Ginn and Co., 1899.) 



AN examination of this volume gives rise to feelings 

 of both congratulation and regret — congratulation 

 that so admirable a manual for the elementary student of 

 NO. 1577, VOL. Olj 



physical geography has been produced, and regret that .. 

 so little attention is given to the subject in our schools ' 

 and colleges. Rational methods of instruction are now 

 advocated for all the concrete sciences, and are being 

 extensively applied to physics and chemistry ; but geo- 

 graphy has only been very slightly benefited by the 

 pedagogic reforms of the last decade, and in the majority 

 of our secondary schools it is still represented by defini- 

 tions, outline maps, uninteresting statistics, and lists of 

 names which make no real impression upon the minds 

 of the pupils. Physical geography, the elements of 

 which should be presented at the very beginning of the 

 study of the earth, is usually neglected altogether, or 

 taught in a fashion that /ails entirely to place pupils in 

 the receptive intellectual attitude reached after sound 

 instruction in any science. 



The present position results chiefly from the want of 

 teachers with a broad conception of the field of geo- 

 graphical science. Every teacher is supposed to be 

 qualified to give instruction in geography ; and if the 

 word merely signified the description of the political 

 divisions of the earth, any one could put pupils in the 

 way of acquiring that information. But, rightly defined, 

 geography should be the consideration of the earth as 

 the abode of man, and it should comprise the elements 

 of astronomy, physics, meteorology, botany, zoology, and 

 ethnology, as well as knowledge of commerce and 

 government. To present the subject in these broad 

 aspects, the teacher must be inspired by the scientific 

 spirit and have given personal attention to the facts and 

 phenomena of nature ; and where such teachers are not 

 available instruction in geography cannot proceed on 

 scientific hnes. 



The volume under notice provides an admirable means 

 of improving geographical teaching. Prof. Davis is not 

 only an expert in most of the branches of physical 

 geography ; he is also a practical teacher who has de- 

 voted much attention to the educational side of the 

 subject. The result is that, with the assistance of Mr. 

 Snyder, he has produced what is certainly one of the 

 best manuals of physical geography ever published. The 

 book is well planned, trustworthy, clearly written, and 

 liberally illustrated ; it presents the facts of physical 

 geography in such a way that the reader sees them as 

 part of an organic whole — as organised knowledge which 

 constitutes science. The facts are traced backward to 

 their causes and forward to their consequences ; indeed 

 the phrase "causes and consequences" has served as a 

 touchstone by which the treatment of each subject has 

 been tested. 



The order of treatment is the earth as a globe, the 

 atmosphere, the oceans, and the lands. These facts are 

 not, however, treated in equal detail ; indeed, the last 

 part occupies more than four times the number of pages 

 devoted to the three preceding parts taken together. 

 From this it will be seen that the book is not con- 

 cerned with physiography as it is usually understood 

 in this country, but with the science of land form 

 In physiography the student receives practical instruc- 

 tion in physics, chemistry, astronomy and cognate 

 sciences before he considers atmospheric phenomena 

 the circulation of water on the land, the earth's solid 



