644 



NATURE 



[July 21, 192 1 



theories, comparing as it does, in particular, the 

 services of mechanical and mathematical theories, 

 is of great interest. The aspect of a theory 

 brought out so strongly by Mendeleeff's words, 

 " By a theory I mean a conclusion drawn from 

 the accumulated facts we now possess which en- 

 ables us to foresee new facts which we do not 

 yet know," might, perhaps, have been more 

 emphasised. 



Of Mill's canons of induction our author dis- 

 poses in a very workmanlike manner. The chapter 

 on chance and probability seems to us to con- 

 tain some very sound and valuable remarks on 

 the fundamental assumptions of this difficult study. 

 An example in this chapter has already drawn 

 down the wrath of an eminent mathematician ; 

 this example, which deals with the drawing of a 

 given ace from a piquet and a whist pack side 

 by side, at first sight appears to be made the 

 ground of a somewhat perverse comment on 

 ordinary reasoning, since it is admitted that the 

 ordinary estimate of the probability is " right " ; 

 but actually it leads up to a point of some import- 

 ance. The usual assumption is that the choice of 

 either pack in the first instance is equally prob- 

 able; but this does not follow from first principles 

 unless further conditions as to blindfolding, and 

 so on, are introduced. Actually, the chooser 

 might well be considerably influenced in his choice 

 by the relative size of the packs ; and what is 

 really the probability of drawing a given ace is a 

 matter for experiment under conditions rigorously 

 specified. The point brought out, though perhaps 

 not that on which most stress is laid, is that 

 the given conditions are often not stated precisely 

 enough in problems of this nature. 



The discussion on probability is continued in 

 the second part, where the subject of errors of 

 measurement is investigated. The criticism here 

 is searching, but is not likely to be accepted in 

 its entirety without debate : the suggestion that 

 the physicist will more frequently find distribu- 

 tions in his notebooks which give a curve like the 

 letter "A" with its top removed than a Gaussian 

 curve will scarcely be accepted. No doubt his 

 arguments will receive more detailed consideration 

 from the experts than is possible here. 



The chapter on units and dimensions deserves 

 particular attention. It contains valuable observa- 

 tions on no-dimensional magnitudes and formal 

 constants, as well as some startling suggestions, 

 including what seems to be an implication that 

 the arrangement of the terms in a dimensional 

 equation is of importance. 



Dr. Campbell writes with enthusiasm and 

 seeks the combat where it is thickest. The chief 

 fault of his style arises from a desire to deal with 

 NO. 2699, ^'OI^- 107I 



every possible comment that might be raised and 

 hence to labour points which are sufficiently obvi- 

 ous. There is a certain lack of co-ordination^ 

 which he acknowledges ; in fact, one of the things 

 which render it an ungracious task to criticise is 

 that the author is keenly alive to deficiencies in 

 the book, and is always anxious to point them out 

 himself. The work gives the impression of bril- 

 liant and informed table-talk on the basis of 

 physics carried on evening after evening, the 

 amount of thought devoted to any particular point 

 depending largely on the mood of the moment. 

 There is little doubt that most readers will find 

 Dr. Campbell provocative in parts, but, whatever 

 else he may provoke, he provokes thought. 

 Finally, it is a great feat to have assembled so 

 much interesting matter, and to have put to- 

 gether a book containing so much fresh thought 

 on a subject of fundamental interest. It is to 

 be hoped that the interest taken in this book will 

 prove amply sufficient to encourage the author 

 to bring out the contemplated remainder of the 

 treatise. E. N. da C. Andrade. 



Mind and Brain. 



Ill Search of the Soul and the Mechanism of 

 Thought, Emotion, and Conduct. By Dr. B. 

 Hollander. Vol. i. : The History of Philosophy 

 and Science from Ancient Times to the Present 

 Day. Pp. x4-5i6. Vol. ii. : The Origin of 

 the Mental Capacities and Dispositions of Man 

 and their Normal, Abnormal, and Supernormal 

 Manifestations. Pp. vii-l-361. (London: 

 Kegan Paul, Trench, Trubner, and Co., Ltd. ; 

 New York: E. P. Dutton and Co., n.d.) 

 2I. 2s. net two vols. 



THAT the psychological phenomena loosely 

 grouped together under the term " mind "" 

 are in some way correlated with the physiological 

 activities of the brain is a proposition which may 

 be regarded as having been generally accepted for 

 more than a century past; the question, however, 

 as to what is the nature of that correlation still 

 remains unsolved. The fact that this particular 

 question must be allowed to lie in abeyance does 

 not militate against the very legitimate attempt to 

 locate differentiated mental functions in relation to 

 the various structural parts of the brain, and as a 

 matter of course many observers have sought to 

 produce a psycho-physiology of the brain. 



The human brain is chiefly remarkable, from, 

 the point of view of comparative anatomy, for the 

 extraordinary development of the cerebral hemi- 

 spheres, which conceal practically all the other 

 portions of the brain. They constitute virtually 

 a great pall consisting of a grey surface or cortex, 

 composed of many layers of innumerable nerve- 



