■808 



SCIENCE. 



[N. S. Vol. V. No. 125. 



precision required in its execution No labora- 

 tory in which such a book is likely to be used 

 can fail to do better in the way of a simple 

 pendulum than ' a string and a leaden bullet ; ' 

 and successive values for ' g ' ought not to 

 differ from each other by as much as one and a- 

 half per cent. 



Professor Dolbear's little book on the First 

 Principles of Natural Philosophy might impress 

 one as being, in text as well as title, a protest 

 against the progress of physics during the past 

 quarter of a century. It is true that there are 

 some things in it that were not known twenty- 

 five years ago, but not many. Throughout the 

 volume the author makes no mention of the 

 metric units of mass and length, on the use of 

 which so much of modern physics depends, de- 

 claring himself very decidedly against them in 

 his preface. This naturally results in much 

 confusion and difiiculty, especially in the mat- 

 ter of electrical measurements. The funda- 

 mental principles of dynamics are presented in 

 a confused and uncertain manner, and accuracy 

 is sacrificed often apparently to secure sim- 

 plicity. 



Mr. Stone's Experimental Physics is evi- 

 dently the outcome of his desire to satisfy the 

 demands of the Harvard College entrance 

 examinations in physics. The well-known 

 ' forty experiments' prescribed by the Har- 

 vard authorities are included with a consider- 

 able number besides. The author says that 

 the book is the result of nearly ten years' ex- 

 perience in teaching experimental physics, but 

 he gives no hint as to how many years he has 

 spent in studying the subject. The latter 

 query is suggested by the numerous evidences 

 of ignorance, or of extremely careless writing, 

 which are scattered through the book. 



Without raising the question of the soundness 

 of the method adopted, which is that of labora- 

 tory work from the start, and before the stu- 

 dent knows the simplest elements of his subject, 

 it is sufficient to note that if the experiments 

 outlined are made with care and reasonable 

 precision very many of them will entirely dis- 

 prove the principles they are intended to es- 

 tablish ; while, on the other hand, if many of the 

 principles laid down are accepted without care- 

 ful tests the student will acquire many quite 



erroneous notions regarding the properties of 

 matter and the principles of physical science. 

 This is a serious indictment, but in its support it 

 is only necessary to refer to the assumption that 

 the breaking weights of wires of the same ma- 

 terial are proportional to their cross sections ; 

 the announcement of the ' law' that for a 

 given tension the elongation is inversely pro- 

 portional to the area of the cross section of the 

 wire, and other things similar in character. If 

 the author had actually experimented on these 

 things, instead of trying to tell others about 

 them, he would not make such utterly absurd 

 statements. The book contains many excellent 

 problems, and now and then a good suggestion 

 as to experimental methods. 



There are many books of this type, and they 

 all enjoy a common distinction of being, on the 

 whole, more likely to create a distaste for real 

 work than an appreciation of, and a love for, the 

 science of physics. The study of the subject is 

 made largely mechanical by having every ex- 

 periment explained in the utmost detail, so 

 that the student has nothing to do but to put 

 the various pieces that he finds, carefully 

 placed upon his desk, in the several relations 

 explained in the book, and then note the result 

 which the book tells him will follow. Occa- 

 sionally some unfortunate may note that the 

 prescribed result does not follow, but that some- 

 thing else happens, and in good time he may 

 become a physicist, if not too thoroughly in- 

 structed. 



It ought never to be lost sight of that the 

 real value of instruction in physics, and espe- 

 cially in experimental physics, lies in teaching 

 people to think. As a means of accomplishing 

 this it has, perhaps, no rival, but both in and 

 out of books the shadow is too often mistaken 

 for the substance. 



Antropologia della Stirpe Camitica. By Giti- 

 SEPPE Sekgi. Torino, Fratelli Bocca. 1897. 

 8vo. Illustrated. Pp. 426. 

 This well-printed volume is part of an ex- 

 tensive study of the anthropology of Africa, 

 projected by the distinguished professor of the 

 University of Rome. It is devoted to the di- 

 visions, characteristics and distribution of that 

 branch of the human species which, following 



