•74 



NATURE 



[August io, 191 i 



of the form k = a+bT, which he applies to the calcu- 

 lation of entropy. He shows that when expansion 

 follows the path (called a " polytropic " path) p v» = 

 constant, the rate of heat absorption or emission is 

 directly proportional to the temperature change, and the 

 author therefore deduces that the "specific heat " must 

 be constant along any such path. This seems confusing 

 when it is realised that this particular proof rests on 

 the hypothesis of a constant specific heat, but investi- 

 gation shows the confusion to be due to a somewhat 

 loose use of the term "specific heat." This may prove 

 a stumbling-block to some readers. After a careful 

 and necessarily compressed account of the basic 

 thermodynamic laws, the author gives an account of 

 the properties of entropy, and of the limitations to be 

 observed when non-reversible cycles are being studied. 

 He rightly points out that many of the most important 

 engineering processes are not even "cyclic," to say 

 nothing of their not being "reversible." He re- 

 marks — 



"A careful distinction should be made at this point 



between the expression j — and the term 'entropy.' 



The former is merely an expression for the latter 

 under specific conditions . . . perhaps the most general 

 statement possible for the second law of thermo- 

 dynamics is that all actual processes tend to increase 

 the entropy; as we have seen, this keeps possible 

 efficiencies below those of the perfect reversible en- 

 gine." He concludes, however, that "most operations 

 in power machinery may, without serious error, be 

 analysed as if reversible; unrestricted expansions 

 must always be excepted. The entropv diagram to 

 this extent ceases to have an automatic' meaning." 



We seem here to be getting nearer to the desired 

 harmony between the various views, as to the nature 

 of entropy and its utilisation, which have been ex- 

 pressed in the past. Brief as the author has found it 

 necessary to make his description of the action in a gas 

 producer, he has been able, we are glad to see, to 

 consider the important case where exhaust products 

 are employed instead of steam as a "heat reservoir," 

 and he gives on p. 153 an interesting diagram com- 

 paring the two alternatives, which should prove very 

 useful in practice. 



It may be a surprise to some readers to find that, 

 :ontrary to the usual custom, the internal combustion 

 sngine is dealt with before the steam engine ; but since 

 the study of gases is easier than that of vapours, it is ' 

 in reality a rational sequence to adopt. The section 

 an the steam engine is very complete, and includes 

 an account of wire-drawing, condensation, steam- 

 jacketing, superheating, compounding, the use of 

 turbines, boilers, drafts, fans, chimneys, stokers, 

 ;conomisers, pumps, and injectors. It would have 

 seemed rash to forecast that so many subjects could 

 be treated in one book, but the author has succeeded 

 in including all this, and more, in his four hundred 

 and forty pages. 



In conclusion, we have no hesitation in welcoming 

 the book as a valuable addition to the literature of the 

 subject. It will be of special use to scientific en- 

 gineers, to practical physicists, and to that growing 

 student class which aspires to become the one or the 

 oilier. 



NO. 2l8o, VOL. 87] 



THE SOURCES OF EDUCATIONAL THEORY. 



The Child's Inheritance: its Scientific and Imagina- 

 tive Meaning. By Dr. G. Macdonald. Pp. xii-t- 

 339. (London : Smith, Elder and Co., 1910.) Price 

 12s. 6d. net. 



rHIS book, which some readers will find prolix 

 and whimsical, but all must acknowledge to be 

 eloquent and sincere, seeks the ideal form of the 

 educational process as a development of the child's 

 racial inheritance. 



" In the understanding of the child's inheritance 

 both the poet and the biologist are worth deep and 

 close study, not because they are necessarily antagon- 

 istic, but because, if they understood each other better, 

 the gain to education would be incalculable." 



For this reason the author directs us to Words- 

 worth's "Prelude" and Weismann's theory of the 

 continuity of germ-plasm as the best sources of educa- 

 tional doctrine. The synthesis is original, and Dr. 

 Macdonald is probably right in thinking that Weis- 

 mann "would find his place somewhat unexpected 

 while standing as the poet's squire." He would pos- 

 sibly be still more astonished at his proximity to 

 William Blake, who is also repeatedly quoted. 



Dr. Macdonald has published elsewhere a lecture 

 on "The Sanity of William Blake." The citations 

 in the present work certainly indicate that a teacher 

 with the right temperament may learn much profes- 

 sional wisdom from the mystical poet. With the aid 

 of these oddly consorted authorities the author dis- 

 cusses the nature and interaction of the child's endow- 

 ment and environment. The former is "the old world 

 within " — the epitome, as Haeckel taught, of phylo- 

 genesis. The latter is "the new world without," 

 which, by imitation, by suggestion, and in other 

 ways, moulds the plastic substance of the child's 

 mind. Examining in further detail the interplay be- 

 tween these fundamental factors, the author finds two 

 processes or aspects of mental growth to be of the 

 first importance — expression and imagination. The 

 chief means of expression is "the service of the hand." 

 The discussion of this topic is rather one-sided, but 

 is nevertheless an interesting and valuable contribu- 

 tion to a subject of much present importance. 



The chapter on imagination — described as " that 

 something in the child which recognises the shining 

 light in all things living " — gives occasion for some 

 not ill-founded criticisms of existing views of man's 

 nature and of educational practices based on them. 

 The chapter headed " Faith and Recreation " contains 

 an admirable doctrine of the functions and value of 

 play. In an intermediate chapter "On Specialisation," 

 the author is led by his favourite thesis that mental 

 life is more than "an assembly of various functions" 

 to combat vigorously any form of specificity in educa- 

 tion. It is perhaps unfortunate that a criticism of 

 education, which, though ill-balanced and occasionally 

 extravagant, must on the whole command respect, 

 should lead to this position. For many of us feel that 

 vocational education, properly understood, is the most 

 hopeful means of giving the child effective possession 

 of his inheritance. 



T. P. V 



