378 



* KNOVv^LEDGE ♦ 



[Mabcu 3, 18S2. 



much mori' — tho bi'jjinnpr hiM his att<»ntion first dirod^-d 

 to a K*"'"''-'' proposition, which is oft<Mi far from cli-ar. 

 Tlio lonriii-r is always rnadior to imdiTstand particrulars 

 than gcniTals : Imt in Kiioli<I ho iios to givt- muoh 

 thought to the iut4'rpn-Lation of a statement couclit-d in 

 torras which scpni to him vaguo and perjilexiiij;, until 

 ho has read their int<Tprptation in the heginning of 

 the demonstration. Then, if he really wants to understand 

 what he is aliout, he goes l>aek to the enunciation. Tliere 

 is no reason wliy this roundabout course should be fol- 

 lowed. Instead of l)(!ginning, for instance: "If two 

 triangles have two sides of the one e(|ual to two sides of 

 tlie other, each to each, and if the angle contained by tlie 

 two sides of the one l)e equal to the angle contained by 

 the two sides, e<iual to them, of the otlier," .and so forth — 

 why should not the proportion proceed thus : " If in the 

 triangles A1?(J, DEF, AH is equal to DE, and BC to EF, 

 also the angle ABC equal to the angle DEF," etc. The 

 attempt to interpret the meaning of the enunciation 

 as a general proposition is in reality so much waste 

 labour. It is akin to the waste labour which children 

 at school used to be invited to l)estow on such grammatical 

 propositions as these, ^Vhere contingency and futurity are 

 lioth implied, the verb sliould be in the suV>junctive, instead 

 of being told that such a st^ntence as " If it rains " 

 is correct when you mean " if it is raining now," and in- 

 correct when you mean " if it should rain to-morrow." Of 

 course, the principle of these general propositions is sound 

 enough, if we are writing for logicians, just as it is sound 

 enough to define a piano superficies as one " in whicli any 

 two points being taken, the straight line between them lies 

 wholly in that superficies." But definitions and enuncia- 

 tions of logical precision are not for beginners. We wonder 

 what Euclid would Iiave said if he had been told his treatist; 

 ■would be used for learnii\g first' lessons in geometry ? It 

 is a pity, we think, that Mr. Coiistable did not simplify his 

 l)Ook a little in this direction, having no enunciation 

 distinct from the explanation of the figure. Even for 

 more advanced mathematicians, enunciations are emphatic 

 nuisances ; the time given to interpret the roundabout 

 phrases, necessary when a figure is not referred to, is just 

 so much time wa-sted. So is the time wasted which is given 

 to the wording of such enunciations. Often, despite the 

 time thus wasted, the enunciation is not intelligible till a 

 figure is drawn illustrating it Thus " if from two dia- 

 metrically opposite points on the circumference of a circle 

 perpendiculars be drawn to a straight line outside the 

 circle, the sum of these perpendiculars is constant." How 

 are we to intorprert; this 1 Constant wherever the line may 

 be, or whatever the size of the circle 1 or in whatever 

 direction the diameter is drawn ? or may any two of these 

 vary ? or all three ? Still, this happens seldom in the book 

 before us, and the use of enunciations is common to a great 

 many treatises on geometry. The propositions are clearly 

 and simply dealt with, and the work is very carefully 

 printed and illustrated. In proposition 18, p. 13-5, it 

 .should be noticed that the construction fails if triangle 

 SPR is less than one-jitli part of the quadrilateral. There 

 are, however, very few mistakes in the book. 



DR. LUYS ON THE BRAIN.* 



Dr. Livs has adoijted a method of cerebral research 

 which he regards as of extreme value. He makes regu- 

 larly stratified sections of the cerebral tissue, and has these 

 faithfully reproduced by means of photography ; he then 



• " The- Brain nnd its Piinctions." By J. Leys, Physician to the 

 Hospice (ic la Snlputrit^ro. (London.) 



employs successively-graduated magnifying powers for the 

 represi-ntation of certain details. By these new methods 

 he has been al)le, he considers, " to ))enetratc further into 

 the- still unexplored regions of the nervous centres, and, 

 like tt traveller returneil from distant lands, to l)ring back 

 correct views and faithful representations of certain terri- 

 tories of which our predecessors caught scarcely a glimpse." 

 After carefully surveying the elementary properties of the 

 n(Tvou8 elements, he arrives at the conclusion that it is by 

 means of their combination, and by the harmonious co-ordi- 

 nation of all their truly .specific energies, that the brain 

 feels, i-emembers, and reacts ; and that, in fact, they are 

 the oidy living forces present, always imderlying the infi- 

 nite series of operations which the brain everj' moment 

 accomplishes ; and that, in fact, without them, that admir- 

 able and complex apparatus, at once so delicate and so 

 siniple, would be as absolutely without life and without 

 movement as the earth would be, without the sun. 



The present work, in which Dr. Luys thus endeavours 

 to carry the data of contemporary physiology into the 

 hitherto uninvaded domain of speculative psychology, is 

 full of interest, despite its occasional too technical ter- 

 minology. The Iiook is in part suitable only for medical 

 men, but in greater part it is easily to be understood by 

 the general reader. We may not accept Dr. Luys' opinion 

 that " from this time forth a true physiology of the brain 

 has been established as legitimately as the physiology of 

 the heart, lungs, or muscular system," but he has done 

 much to show that we are fairly on our way towards this 

 result, "a consummation devoutly to be wished. ' 



Some of the facts used by our author to illustrate his 

 views are very interesting when thus viewed. Such, for 

 instance, are the familiar phenomena of association. " It 

 is sufficient," as he says, " to see an object or a person — to 

 hear a name pronounced accidentally, to smell an odour — 

 in oi'der to feel arising within us a series of ideas which 

 arose at the moment when this impression was at first per- 

 ceived by us. We all know how frequently in current 

 conversation a word — a simple sound — causes the primitive 

 direction of our ideas to diverge." This curious property, 

 which sensorial impressions, received at the same time, 

 possess, and which constitutes, as it were, natural families 

 among them, is a gi-eat resource in the education of the 

 intellect, and the methodic cultivation of the faculties. 



Among the singular facts referred to in this work may 

 be mentioned the experiments of Charles RoViin, on the 

 corpse of a decapitated indi\-idual (Ch. Robin, '' Journal de 

 I'Anatomie, Paris 1869, p. 90). They showed that the 

 automatic activities of the spinal cord in man may continue 

 to exhil>it undiminished energy, and power of co-ordinatious 

 in the form of regularly-associated movements with a 

 definite object (such as movements of defence made bj" the 

 hand after a cutaneous excitation), these being performed 

 with as much regularity as though the brain had directed 

 them. 



GANOT'S PHYSICS.* 



A BOOK SO well known and so widely valued as Ganot's 

 Physics, scarcely requires the evidence which the issue of 

 a tenth edition atibrds, to show that it is thoroughly 

 sound and ti'ustworthy. It is a text-book which fidtils the 

 purpose which we have set before us in Kxowledce, being 

 clearly worded, yet exactly described. It is very well 

 illustrated, and the various physical subjects dealt with in 



• " Elementary- Treati.ie on Physics. Experimental and Applied." 

 For tlie Use of Colleges and Schools. Translated and edited from 

 Oanot's " £l6ments de Physique.'* By E. Atkinson, Ph.D., F.C.S. 

 Tenth edition. (Longmans A Co., London.) 



