5»o 



NATURE 



[February 15, 19 12 



mental changes on assimilation and the like, and the 

 influence of psychical impulses and needs relating to 

 tho external conditions of life. In both these ways a 

 " somation " (corresponding to a somatic modification 

 of most authors) may arise; it is an ectogenous change 

 in contrast to an autonomous mutation. The endo- 

 genous secondary principles, which are also called 

 entropic, include amphimixis and death. 



THEORETICAL AND PRACTICAL PHYSICS. 



(i) A Text-book of the Principles of Physics. By Dr. 

 A. Daniell. New and revised edition. Pp. xxv + 

 819. (New York : The Macmillan Co. ; London : 

 Macmillan and Co., Ltd., 191 1.) Price lys. net. 



(2) A Textbook of Physics. By Prof. L. B. Spinney. 

 Pp. xii+605. (New York : The Macmillan Co. ; 

 London: Macmillan and Co., Ltd., 1911.) Price 

 12s. net. 



(3) Principles of Physics : Designed for Use as a Text- 

 book of General Physics. By Prof. W. F. Magie. 

 Pp. ix + 570. (London : G. Bell and Sons, Ltd., 

 191 1.) Price 75. 6d. net. 



(4) Treatise on Practical Light. By Dr. R. S. Clay. 

 Pp. XV + 5 19. (London : Macmillan and Co., Ltd., 

 191 1.) Price 105. 6d. net. 



(i) TT is presumably the duty of a reviewer to try 



i 



m reading a text-book to take up the point 



of view of the students for whom it is primarily 

 designed. This attitude it is not at all easy in many 

 cases to assume. But the third edition of Dr. 

 Daniell's text-book scarcely admits of doubt in this 

 respect. Regarded from a purely physical point of 

 view, the book undoubtedly contains much useful 

 information, notwithstanding the fact that it is pre- 

 sented in a peculiarly disjointed fashion. But to 

 propose it as being suitable for medical students seems 

 very misleading. Those who are experienced in 

 teaching medical students, or, at any rate, the majority 

 of them, know with what simplicity the principles of 

 physics must be treated. The subject is one which 

 the students themselves think is foreign to their 

 medical course, and the complexity of detail with 

 which this book abounds would surely make them 

 adhere more strongly than ever to that opinion. But 

 apart altogether from the question of suitability for 

 any special class of students the book is in several 

 other respects open to serious objections. In the first 

 place, the unfortunate tendency in many recent 

 physical text-books of quoting unproved numerous 

 mathematical formulae is especially prominent in this 

 particular case. This is, in all probability, the main 

 cause of the disjointed nature of the text already 

 referred to. It must be admitted, of course, that such 

 procedure is occasionally inevitable and even desir- 

 able, but when it becomes the rule and not the excep- 

 tion, it encourages students to regard physics as a 

 series of formulae to be committed to memory, and 

 having no logical sequence. 



Further, the mode of statement is often peculiarly 

 involved, and sometimes inexact. The latter is illus- 

 trated by the statement that "a body free to fall in 

 vacuo would be subject to a constant downward 

 acceleration of about 981 cm. per sec, or 32*2 feet per 

 NO. 2207, VOL. 88] 



sec" — a statement quite in keeping with the un< 

 vincing way in which the distinctions between vekx... 

 and acceleration have been previously treated. The 

 following also is surely a rather extraordinary vi- 

 to express : — " Kinetic friction is accordingly no; 

 Force; it is a Resistance or Reaction." 



The present edition has a supplementary chapter 

 radio-activity and kindred subjects added. Attention 

 is directed to the chief points in recent work, but the 

 numerical data in connection therewith have scarcely 

 been brought up to date, the old value 34 x 10-" ES. 

 being given, for instance, as the unit of electric; 

 The author has also adopted a uniform notation, anu 

 gives an index of symbols at the beginning of the 

 book, but although, in this index, io» is defined as 

 being equal to 1,000,000,000, we frequently find very 

 large numbers expressed in the uncontracted form. 

 The arrangement of the mathematical treatment is 

 also unfortunate from the point of view of facility in 

 reading, being printed in small type, and from line 

 to line, just like the ordinary text. 



(2) Prof. Spinney's book will without doubt serve 

 admirably the purpose for which it has been written. 

 In nearly every respect it fulfils the necessary- condi- 

 tions. Being written for engineering and technical 

 students entering upon a course of physics, it deals 

 in a straightforward and logical way with the various 

 sections into which the subject is usually divided. 

 As is to be expected, particular prominence is given 

 to mechanics, the principles of which are illustrated by 

 familiar phenomena and practical contrivances. 

 Although the mathematical treatment is intentionally 

 limited, what is given is exact, and involves no blind 

 learning of formulae. Also, notwithstanding the pro- 

 fessedly elementary character of the work, the author 

 contrives to convey clearly the underlying principles 

 of such subjects as surface tension, kinetic theory 

 of gases, and polarisation of light in a way not often 

 achieved. To each chapter is appended a series of 

 numerical examples; the printing and arrangement -'^ 

 paragraphs and chapters are excellent, and the he; 

 tvpe used for the more important statements is a 

 distinct gain. The diagrams have evidently been 

 carefully prepared, and are reproduced in a manner 

 quite above the average. To all students desiring 

 a thorough introduction to the science of physics, 

 whether they be engineering students or not, this 

 book can be unhesitatingly recommended. 



(3) In some respects this book is unique. On 

 several nrevious occasions have historical treatises on 

 special parts of physics been published, but no general 

 elementary text-book of physics based upon a 

 historical outline has until now, we believe, appeared. 

 The author's chief reason for adopting this mode of 

 procedure — and it seems to be a good one — is that it 

 directs attention to the lines upon which discovery 

 has proceeded, and trains the mind of the reader 

 in the processes which may lead to further discoveries. 

 Whether this be the case or not, it is certain that 

 the historical treatment makes the subject eminently 

 readable, particularly to those somewhat acquainted 

 already with the principles of physics. From the 

 point of view of the beginner, however, difficulties 

 might arise owing to the historical sequence necessitat- 



