562 



NATURE 



[January 20, 19 16 



and that the instincts should be linked on to 

 reason and the finer feelings so that the best in 

 us may inhibit the worst. 



The author makes a useful biological contribu- 

 tion to the problem of education, and has a whole- 

 somely strong faith in the importance of "nur- 

 ture," in the widest sense, in developing the 

 individual's hereditary "nature." We would 

 point out, however, that while Dr. Macnamara 

 starts with Lloyd Morgan's clear-cut conception 

 of instinct, he does not consistently adhere to it, 

 and often uses the term instinctive very loosely ; 

 that he seems at times to exaggerate the separa- 

 bility of -instinctive and intelligent faculties in 

 children, for they seem to us to be very intimately 

 blended ; and that he gives glimpses of a quite un- 

 tenable theory of energy overflowing or irradiat- 

 ing from one part of the nervous system to 

 another so as to maintain a state of equipartition. 



Dr. Macnamara was investigating and writing 

 half a century ago, and we do not wonder that 

 he has overlooked a number of typographical 

 etrors, such as "philogenetic," and "exasperating 

 sway" (of women) instead of "way," but he 

 should not have passed a sentence like this :— 

 " The Hydromedusae present two main forms, the 

 non-sexual polyps or Hydra, and the sexual 

 Medusae, such as jelly-fish and sea anemones." 

 Here there are at least three mistakes. Nor can 

 we accept the statement that the male stickleback 

 cements grass-stalks together with a layer of 

 mucus exuded from the surface of his bodv. 



INTRODUCTORY TREATISES ON 

 MECHANICS. 

 (i) An Introduction to Applied Mechanics. By 

 E. S. Andrews. Pp. ix + 316. (Cambridge: 

 At the University Press, 191 5.) Price 45. 6d. 

 net. 



(2) An Introduction to the Mechanics of iFluids. 

 By Prof. E. H. Barton. Pp. xiv + 249. (Lon- 

 don: Longmans, Green and Co. , 1915.) Price 

 65. net. 



(3) Experimental Physics : A Text-book of 

 Mechanics, Heat, Sound, and Light. By Prof. 

 H. A. Wilson. Pp. viii + 405. (Cambridge: 

 At the University Press, 1915.) Price 10s. net. 



WRITERS of mathematical text-books on 

 mechanics and of so-called applied 

 mechanics have still much to learn from one 

 another. A too excessive abstract and logical 

 development of the subject by the one tends to 

 make the student lose the sense that it deals with 

 real things ; while evident striving for ultra- 

 practicality by the other, and the looseness and 

 inaccuracy of statement often combined with 

 NO. 2412, VOL. 96] 



it, irritate him. On the one hand the ordinary 

 student is bored, and on the other puzzled to 

 death. For the difficulties which the industrious 

 student of average ability experiences are more 

 frequently than otherwise due to the fact of his 

 having too logical and clear a mind, or rather 

 perhaps to possessing a mind which requires 

 logical presentment. To a certain extent the 

 three books before us illustrate the above remarks 

 in one direction or the other. 



(i) That the first author would generally agree 

 with them is apparent from his remarks in the 

 preface that the older form of text-book was too 

 much a kind of exercise ground for algebraic 

 manipulation, and that many of the more modern 

 give too much engineering application of the prin- 

 ciples without sufficient explanation of those prin- 

 ciples. And yet in reading through his attempt 

 to strike the happy mean, one is constantly meet- 

 ing statements which, though not quite wrong, 

 are certainly not quite right. The following are 

 a few samples. On p. 18 the principle of 

 moments follows from Newton's first law of 

 motion, because, since it does not change its 

 state of rest, there is no tendency to rotate about 

 any point. Two pages before it was given as a 

 definition that this tendency is measured by the 

 moment. It requires some thought on the part 

 of the student to find that really he has been 

 deceived into thinking that the principle is proved. 

 On p. 17, "so long as we deal with forces in one 

 plane, moments are scalar quantities." The 

 student is brought to a stop with the query why 

 the sc?larity of the moment of a force should 

 depend on the nature of other forces with which 

 it has notliing to do. (Owing to an oversight also 

 here the example given does not agree with the 

 direction of the forces in the diagram.) On p. 40 

 " we may point out that when in ordinary par- 

 lance we speak of power we really mean energy." 

 On p. '139 "stress may be defined as the force 

 between the molecules of a body brought into 

 play by the strain." On p. 124 "inertia is the 

 property of a body which resists a change of 

 motion" recalls Maxwell's classical illustration of 

 this statement by a cup of tea resisting being 

 sweetened by the sugar put into it. It is difficult 

 to see what object is gained by the elaborate 

 drawing of a steamboat on p. 45, or of a traction 

 engine and track on p. 127. 



In spite of these defects, the book can be re- 

 commended for use by engineering students. The 

 substance is well chosen and the treatment ade- 

 quate. A student who has mastered it should 

 have a good working knowledge of the dynamical 

 principles underlying every engineer's work. The 

 first eight chapters are an introduction to 



