Aprils,, 1 88 1 J 



NATURE 



553 



balances the value of the fuller explanation. To explain 

 j'(?//ci'//y we are told that "A solid is characterised by a 

 greater or less degree of rigidity," which in the absence 

 of a separate definition of rigidity leaves us much where 

 we were before. Again, the definition of a liquid is this, 

 "A liquid is characterised by its mobility ; the molecules 

 are free to move about each other, and the liquid takes 

 the shape of any containing vessel," which is equally true 

 of a gas. The proof of the formula ^ = \ft- is clenched 

 by the proposition that " when two sets of variable quan- 

 tities, which are always equal, simultaneously approach 

 their limits, these limits are equal," which is suddenly 

 introduced without any explanation of its meaning. This, 

 in a book intended for beginners unacquainted with the 

 idea of a "limit," would be likely to cause some 

 bewilderment. There is a chapter devoted to Work and 

 Energy, as should be the case with all text-books of 

 mechanics nowadays. 



In the dynamical section there is an entire omission 

 of "Sliding in Chords of a Vertical Circle" and the 

 pretty problems connected with it. In the statics there 

 is no mention of the stability or instability of equilibrium 

 of one curved surface rolling on another. The micrometer 

 screw surprises us by appearing with the mechanical 

 powers alongside of the wheel and axle and differential 

 screw. 



As the compiler has not acknowledged his indebtedness 

 to other works, it is difficult to say how much of this book 

 is original. But we seem to catch echoes of Ganot's 

 "Physics " and of Goodeve's two text-books on Mechanics 

 and Mechanism here and there. For instance, Articles 7, 

 S, 107, III remind one of Ganot, Articles 197, 207, 209, 

 239 of Goodeve. The woodcuts, some of which are good, 

 and others {e.g. those in the chapter on Centre of Gravity) 

 very indifferent, are 190 in number. Some of them are 

 apparently reproductions of woodcuts in English books. 

 We instance Figs. 44 and 175, which are strikingly like 

 Figs. 365 [Joule's apparatus] and 19 [block and tackle] in 

 the eighth edition of Ganot's Physics, translated by 

 Atkinson, and Figs. 142^, 150, 152, 155 (in Dana), which 

 bear a rery close resemblance to Figs. 49, 58, no, 1 13 re- 

 spectively in Goodeve's "Principles of Mechanics," second 

 edition. Fig. 117 in the latter having apparently supplied 

 Dana's three figures, 162, 163, 164 [on Pulleys]. Fig. 145 

 in Goodeve's " Elements of Mechanism," fifth edition, may 

 well have been the original of Dana's Fig. 156. 



It would have been graceful in the compiler of this 

 work to have expressed his acknowledgments to the two 

 excellent little text-books of Goodeve. On the whole, with 

 the reserve above made in favour of the "■ examples," we 

 think that neither English teachers nor English students 

 will be the losers if they continue to use already existing 

 English text-books of Mechanics, and leave this American 

 competitor to find an audience on the other side of the 

 water. 



CONSCIOUS MATTER 

 Conscious Matter ; or. The Physical ami the Psychical 

 Universally in Causal Connection. By Stewart Duncan. 

 (London: David Bogue, 1881.) 



A S the title of this little work sufficiently indicates, the 

 -i^ aim of its writer is to furnish a scientific basis for 

 the theory of materialism in the region of mind. It is 



doubtful whether at this time of day anything very original 

 can be said upon this topic, but Mr. Duncan has suc- 

 ceeded in placing some of the facts in a stronger light 

 than previous writers. The facts to which we allude are 

 those which he calls the " analogies " between forces and 

 feelings. Up to a certain point it is by every one recog- 

 nised that there is some quantitative relation between 

 neurosis and psychosis ; mental processes are universally 

 known to entail wear and tear of cerebral substance. 

 Mr. Stewart Duncan traces this quantitative relation 

 as much into detail as he can, by setting forth in a 

 series of twelve " analogies " the resemblances be- 

 tween forces and feelings. These " analogies " are far 

 from being unopen to criticism severally ; but here we 

 shall merely mention what they are, as there is more 

 important criticism to apply to them collectively. The 

 analogies are that feeling and force are each without 

 e.xtension, both related to matter, have " plurality pre- 

 dicable of them as respects their locality," are diverse, 

 have time-extension or duration, also the quality of degree 

 and capability of being compounded or combined, are 

 respectively transmutable inter se, &c. Doubtless, as 

 Mr. Duncan observes, such analogies, or, as we should 

 prefer to call them, parallelisms, might be largely multi- 

 plied ; but what would any number of such parallelism^ 

 prove ? Not, surely, what Mr. Duncan desires them to 

 prove, viz. that forces stand to feelings in the relation of 

 causes to effects. So far as the tracing of such mere 

 parallelisms is concerned, we might almost as reasonably 

 conclude the recent earthquake at Chio to have been the 

 cause of this review, in that they each possess extension, 

 have diverse parts, and so on. In order to establish a 

 relation of causality we should require to show that the 

 observed parallelism is due to that relation ; we cannot 

 argue from the observed parallelism as itself sufficient 

 proof of such relation. Were this not so, there would be 

 no need for Mr. Duncan or any one else to write a book 

 on "The Physical and Psychical Universally in Causal 

 Connection " ; for as the fact of a constant parallelism 

 between neural processes and mental processes is now no 

 longer an open question, were mere parallelism sufficient 

 to establish proof of causality, materialism would now be 

 a demonstrated theoiy. 



It is needless here to go into the whole question as to 

 the relation of body and mind, or to point out all the 

 shortcomings of materialism as a philosophical theory. 

 But it is a defect in Mr. Duncan's work that he does not 

 attempt to meet some of the most formidable of the diffi- 

 culties with which this theory is beset. Thus he does not 

 consider the fact that what we know as matter and force 

 we know only as affections of mind, and therefore that 

 in all speculations upon the nature and potentialities of 

 the former, we already by implication have necessarily 

 assumed priority of the latter. Nor does he seek to 

 explain the apparent want of equivalency betw^een sup- 

 posed physical antecedents and supposed mental conse- 

 quents—why it is that the brain of a Newton required 

 less nourishment than that of an elephant. Lastly, the 

 greatest of all the difficulties is not adequately treated— 

 that, namely, which is connected with the doctrine of the 

 conservation of energy. Are we or are we not to suppose 

 that thought has a mechanical equivalent ? If materialists 

 say that we are, then thought itself becomes a mode of 



