;o2 



NATURE 



[September 9, 1909 



ticallj' admits Kirchhoff's thoroughly abstract, and so 

 to say a priori, presentation of dynamics to be the 

 best extant from a critical point of view ; and he is 

 conscious of the value of a self-consistent theory which 

 can be applied as at least a first approximation to the 

 actual facts of experience. 



Another advantage of the work is that it does not 

 pretend to be exhaustive. By choosing definite 

 problems (such as impact, for example) and restricting 

 himself to the consideration of really eminent writers, 

 the author is able to give extracts of some length from 

 works of great interest which are not generally 

 accessible. In some ways this is more instructive 

 than any amount of comment can be. 



M. Jouguet stops short of hydrodynamics, and only 

 gives very brief accounts of the principles of least 

 action and least constraint. Otherwise most of the 

 main principles of dynamics and statics are illustrated. 

 The chapters on internal forces are particularlv in- 

 teresting; so is a passage from Euler, which shows 

 that he was vaguely conscious of the difficulties con- 

 nected with the relativity of motion, and the impossi- 

 bility of defining absolutely f^xed axes of reference. 



One reflection is almost certain to occur to the 

 reader of these volumes, namely, that one great ad- 

 vance in the study of natural science has been the 

 rejection of sham proposition about cause and effect, 

 and adequate causes, and so on. It is distressing to 

 find an able man like Wallis giving definitions of the 

 most question-begging description, and stringing 

 together such propositions as " other things being 

 equal, a heavy body has a preference for the path by 

 which it can sink the furthest." However, these early 

 pioneers had a remarkable power of solving problems 

 by elementary principles which they used without 

 being able to express them in a proper, or even intelli- 

 S'ihle way; and the modern theories of light and elec- 

 tricity once more illustrate the curious paradox that 

 theories based on the undefined and.undefinable have 

 the power, not only of simplifying our accounts of 

 phenomena, but also of suggesting paths of discovery, 

 and leading to larger control of the energy surround- 

 ing us. 



If -M. Jouguet 's work reaches a second edition, he 

 will doubtless correct " BernouiUi " to "Bernoulli." 

 In a work of this kind it is rather irritating to find 

 this time-honoured blunder repeated once more. 



G. B. M. 



ORGANIC MEMORY. 

 Die mncmischcn Empfindiingen in ihren Beziehungen 

 zu den Onginalempfinditngen. By Prof. Richard 

 Semon. Pp. xv + 392. (Leipzig: W. Engelmann ; 

 London : Williams and Norgate, 1909.) Price 

 9 marks. 



HTHE theory of the Mneme, propounded by Prof. 

 -L Semon, has attracted the attention both of 

 psychologists and of those naturalists who are in- 

 terested in the profound problems of hereditary trans- 

 mission. It is founded on the statement, which every- 

 one is ready to admit, that a stimulus must affect 

 the quality of living matter in such a \<-ay that the 

 matter is not the same as it was before the stimulus 

 NO. 20S0, VOL. 81] 



acted. A permanent change, which, in a sense, may 

 be called a memory, has been effected, or, to use the 

 terminology invented by Semon, the action has been 

 engraphic and the change itself is an engram. Re- 

 peated stimulation will make the engram more last- 

 ing. All stimuli then produce engrams, and the sum 

 of the engrams of a living being is its mneme. Com- 

 plex stimuli cause complex engrams, and if there is, 

 under the action of some stimulus or other, a revivifi- 

 cation of the complex engrams, then a condition 

 termed ecphoria is produced, and the assemblage of 

 engrams is ecphorized. Jf the new stimulus is in 

 concord with the awakening of the complex engrams, 

 this concord is termed by Semon homophonia, but if 

 there is a discord, the homophonia may be restored 

 in the case of psychical processes, by an introspective 

 activity of the power of attention, or, in the case of 

 a living organism, by regenerative processes acting 

 ontogenetically, or by adaptation to the new conditions 

 acting phylogenetically. 



In this volume Prof. Semon discusses the theory 

 with great clearness and commendable brevity, and 

 he gives many illustrations. The theory may help 

 to explain certain peculiar nervous conditions, as has 

 been suggested by Dr. August Forel in his book on 

 " Hypnotism." On the other hand, it may be of 

 service to the naturalist in his ceaseless efforts to 

 explain heredity, as was so forcibly put by Prof. 

 Francis Darwin in his Dublin address to the British 

 .Association last year. Thus a stimulus may produce 

 effects \yhich radiate from the organised matter first 

 affected to organised matter throughout the whole 

 organism, either by nerve paths or by proplasmic 

 intercellular filaments, and in this way faint engrams 

 may be made on the matter of the reproductive 

 elements, ova or spermatozoids. In some such way 

 we may account for the transmission of acquired 

 characters, a mode of thought, however, only to be 

 ridiculed by those who hold that acquired characters 

 are never transmitted. It may be said with much 

 cogency that such a theory is only another method 

 of arranging items of knowledge in one's mind; it is 

 only an aid to memory and thought, without being a 

 step towards an explanation. Although founded on 

 well-known physiological facts, it rides off on the 

 wings of the imagination, and it may be questioned 

 if it really advances knowledge. Still, an ingenious 

 theory is a stimulus and possibly a guide, and science 

 is indebted to Prof. Semon for stating it in a succinct 

 form in this interesting book. 



John G. McKendrick. 



THE PHYSICS OF THE ION. 

 Lcs Decotivertes moderncs en Physique. By Dr. O. 

 Manville. Deuxieme edition. Pp. iii + 463. (Paris: 

 A. Hermann et Fils, 1909.) Price 8 francs. 



THE title of this work, " Les D^couvertes modernes 

 en Physique," since it is a single volume by a 

 single author, is obviously incomplete. In effect the 

 book is almost entirely, and might have been with 

 great advantage entirely, confined to the relations 

 between electricity and matter consequent upon the 

 conception of the atomic charge and the isolation 



