Princip der Erhaltung der Energie, und seine Anwendung in der Naturlehre. By I~~i1sJl2?rzischfir. 16 x ZJ ciit ; p p . .I* riiid djj. Z~(~ipzig: L?. (,' . T e i i h ? r t~, 1Sy7. Price ; c,'oth / z Triui-ks.-There can he h i t little rlouht that tlie actaal results of our study of physical science consist essentially i n a more or less exact knoxledge of the relations that measurable quantities hear to one another. -1 treatise designed to present the facts of pliJ-sical science in general

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... . therefore, lie concerned Tvitli these relations thetnselves. together \\-it11 the \rorkitig niethod or ine thods by means of which they ha\-e been discor-ered. Of such nietliods the most significant at present is, unquestional)ly, the energy theory. The procedure of the energy theory cotisists. as el-eryotie k n o~v s , first i n seeking the \~-ork-equir;ileiits of physical trianifestations. aiid then in assert.. ing the constancy of the :ilgetxaic sum of all amounts of wdrk and of workequivalents that undergo change in an>-process considerell. This assertion of conservation rests, of cou-se, upon the principle of the excluded perpetual rioti ion, which \r-e recogiii;:e in its turn as nothing other tlian a siiuple expression of the ultimate scientific postulate that definite relations do subsist airiong the measurable parameters \\-hose clianpes tleterniine physical pheuoniena. . 1 further elernei~t of the energ!: theory is, to he sure. the determination of the potential. and therefore of the corresponding quantit!--coorcliiiate. of any gix-en workequivalent,--i, c . , in hrief, the 'potential theory'. .1ccortliiig tu this. an ideal erposition of the outlines of physical science must either s h o~~. i n historical order, how the energy principle. whether consciously or ~i i i c o~i~c i o~i~l~ applied. has reached its several results : or it must first describe and justify the tiiethotl itself, and thereupon c1eta.J in some logical order the actual applicatioiis of it that have beeii made. Januschke. in his Pt'iti,rip der-E~haZfir7ifi del E ) i e f :~i e , has followed tlie latter, or more deductive. plan ; and it may l~e said that lie has made a brave aiid praiseivorthy attempt to give a connected account of the real facts of physical theory. ' I Im vorliegetideu Buche sollei! Geltimg uiid .-\nwenduIig des Energie-priucipes i n alleti Gebieteii d e r S a t u r l e h r e dargethati werden. E s geht a u s rieljiihrigeii Studien iiber die verwendung des genannte-1 Principes fiir deu hiiheren Uiiterricht hervor [ h e is Director of t h e Ohtw'enlsi.hi~le i n Tesclien]. nlinlich B U S den1 Bestreben. mit Hilfe des Principei nnch einem einheitlichen Plane sowohl die einzeltieii Erscheiuungen eindringlicher LII I)ehniide!ii. ais a u c h d e n Zusarnmenhang derselhen tnijglichst innig E L I gestalten." In the working out of this plan the a~itlior h i s etili\-eiied his text by the addition of considerable interesting and well stated historical itiforination : :md he has simplified things by u+ing the calculus iiotatioii freely, altllough without introducing any extended anal>-tical de\-eloptnents. Of the 450 pages of the I11 his o~\-n xords : hook, 104 are devoted to the dyiianiics of solids ; 20 pp each to the dynamics and statics of liquids aiid of gases respecti\-ely : 69 pp to what are uiifortuiiately termed ' niolecular forces', -namely cohesioii, elasticity. capillarity, and osmotic pressure : 6; pp to heat : 133 to electricity and niagiietisni ; and 2 2 to light. .llthough the book is not a treatise on p h y i c a l clieiriistry proper it is interesting throughout to the physical chemist. antl this is particularly true of the estendecl chapters 011 the 'niolecular forces', on heat, atid on electric currents (really electroclieinistry i . Oiie-compoiient systems are treated i n sorne detail iii the chapter on heat : polycoiiiponent systems. on tlie other hand. are not given aiiythiiig like due comitleration. The tlisappoiiitiiig feature of the work is tlie author's weak grasp of the three great ideas upon which the eiier,gy theor>-is liuilt : the idea of the relativity of physical plietio~neiia : that of the potential. and of tlie correspoiiciiiig quantity-coordinate. of each work-equiralent : aiid the conceptioii that ' bodies' are complexes of sense-elerneiits. K e p r d i i i g the first of these points, the author's vagne idea that ' ' The prohleni of natural science is to gain a n uinclerstaneling of natural plieiionienn" (~2 . 9' contrasts unfavoralily with. for instance, IIach's ' The aim of all [physical] research is to ascertain tlie riiode of connection of the sense-elemelits that constitute iiotlies' , I , p~' , -\vlierel)!-, of course. it is uiitlerstood that these modes of connection are to be espressetl in terms of the physical paraiiieters that are tleteriiiinetl by -are iuinctions oftlie seiise-eleiiieiite. If the author hat1 heen clear on tlie secoiitl point lie could not liave classified forces. tensions. and pressures. iritli theriiioilyiiarIlic temperatures. electric potentials, etc., as 'iiitensity factors' ; for these are not tlie sanie kind of thing at all. -the former are forces. tlie latter are true potentials. He coulll not have fallen into this tlifica1t)iiad he perceived tlie fiuiclanieiital tlistinctioti between work and ~1.ork-equiv~~lents. -the one lieiug the protluct of a force into a change of space, the other the protluct of a potential into tlie change of a quatitity-coorcliiiate. =\tit1 his antiquated nietaphysics. fillally. ( t h e third pLiiiit; is eseiriplifietl liy the naive aiicl helpless reiiiark that I ' The p i~i~~7 n c~/ t ,~ seliseaffecting part of the things aliout us \\-e tertii . . . iirtrtfri-or szhstczirre : spatially liniitecl inatter is called body" ( p . 2 ' . Is this irresponsilile rnetaphysical ghost ' matter' n e w r to tie liaiiishe(1 from anion:: 11s ? . l i i t l \vliy slioultl physicists. of all people. lie the ones to cling so tenaciously to a crude aiitl outworn inaterialism ? Physics, antl cheniistry with it, ha\-e to (lo with lmtlies.they do not have to rlo Tvitli ' iiiatter'. \ l y e inay say of our author. ho\\-e\-er, ant1 w e say it gratefully, that he '. makes 110 u s e of O;tx\\-altl's L-iew that energ>-is a real agent. ' ' Sotwithstaiitlitig the \\-eaknesi of the author's funclarneiital scientific ideas. the general plan of his book is fairly gooel. aii(1 tlie tletnils are, on the whole. clearly aiid sensihly put. -1s a work for geiieral reference, sntl as a presentation of x h a t might almost lie calletl the pli>-sics of physical chemistry, it caniiot but prove a useful hook. J . E . Trez'oi, ~' J I (leo7.g H E~I I I . 15 x 23 ciii ; $# .rii 17ild 370. L e i p z i r : 17ecil r c i i t i Colufl., 18yS. 1 3 i c c : pnfiei, S.60 ~ii~7rk.s,-Iii the course of the \-igorous riiscussioii of the riel\-'eirer-Die Energetik, nach ihrer geschichtlichen Entwickelung. 1 The it,ilics a r e t h e a u t h o r ' i . A 1 7~~t~ B O O~S 38; getics'. carried on in Germany in Isgj-96, chiefly hj-Helm, Roltzmann. and Ostn-ald. Helm announced that he hac1 in preparation a conipreliensive work 011 the historical developnietit of the energy theory. This l011g ;i\raitetl hook is 1 1 0~ out. and its appearance n-ill unquestioiiahly he geete(1 \\-it11 a n-itle-spreatl interest. To allow the auzhor hiniself to speak first for it, we Iirint his preface entire, reserving for our next issue a detailed esaininatioii of the bocly of the. test. fluence of t h e years that have passed sirice t h e excitement of t h e Lliheck days briugs w a rr a u t that its pages will treat quietly of t h e acquisition a u d outgroxviug of opinions, a n d of t h e struggle for truth a u d for recognitiou of error. " 111 a few places, pnrticu1,irly in Part TI. it will b e Iioted. -iiidulgeatly I hope,f r o m t h e halting of the book that it conies f r o m battle. In these places a p p e a r discussiolis that correspoiid in extent neither tc t h e difficulty of t h e que.5tions considel-ed, iior to their infliietice. S o t as iu t h e retnaiuder of t h e !look could t h e allotment of space h e r e be ~overiiecl solely b y at1 estimate of t h e value a n d import of the iiir-estigations presented ; t h e xrriting had to h e done with a view to defense. Energetics, a s it hac del-eloped from t h e days of Robert Mayer to o u r own. is i n its honlo-rneity of cha:acter a uuiqiie kiiid of comprehensive knowledge of uature. Errors and excrescences h a w iiideed a p p e a r e d a t a l l stages of its development. a s is also t r a e of much t h a t f i i~d s general acceptance to-day. But h e w h o h a s a 1 1 appreciation 01 historical derelopment understaiids that useful growths a n d tho>e that require to b e pruued a w a y a r e alike prodiiced b y t h e saiiie fo:-ces. T!:e b o o k I-eyisters protest, therefore, ag:iitist regarding either single i ) r n i~~h r i U I teinporary iniscouceptions a i coustituting t h e true eiiergetici -a i its opponents have sou:ineaiis of undetermined coefficients. .Is a practical method this is eminently satisfactory, hut as a proof it can h a r d lhe accepted as satisfying. The usual proof is deemed too difficult for the average student and is accordingly relegated to the appendix. which also contains a short but serviceahle table of integrals. The distinguishing feature of the hook is tlie thoroughness and clearness with ~l i i c h the fundamental ideas are explained. S o one who studies it should carry awaJ-with him the usual hut erroneoils view that the integral calculus is at best only a peculiarly dismal algehraical exercise. For those whose object is practical this is perhaps the best testbook that has yet appeared. 13; X 21 c m ; p p . x i u n~z d 23s. A i d Saurel The Principles of Theoretical Chemistry with Special Reference t o the Constitution of Chemical Compounds. BJ, 11-n Zfe?irseii. Fij'Yh E d i i i o z . 14 x zo c i i i ; p$. iz' n12d 326. Philnde11)/zitr : L e n Brofhei-s niid Co., rY97. IVice: cZo2/2, $r.cio.--.ls indicated in its title the object of this work is " to point out as clearly as possible the reasons for accepting the prevailing views in regard to constitution. to show that these views are not merely proclucts of the iniagination. but that they are the legitimate results of a profound and comprehensi\-e study of chemical phenoniena. and that they are the simplest views possihle if TW accept as the hasis of speculation the atomic theor-. * ' -2'csil Books 389 By thus limiting the scope of his treatise. and in particular by omitting all therrnodynaniic discussion, and condensing to the utmost all matter relating to the recent advances in phi-sical cliemistr the author has been able to present a selfcontained arid connected accoutit o the most characteristic branch of distinctively chemical theor>-.Inti whether one considers the great practical services rendered to organic chemistry by the theories of constitution, or their almost total want of coiinecrion Tt-ith tlie recent work iii general chemistry. it can hardly he denied that the subject is much better discussed in a volume to itself thanas is the case in oiie well-known workiii a chapter \vedged hetween ' tlie theory of solutions ' and ' the action of mass '. The book begins with the laws of definite and niultirile proportion. " the fundamental laws of chemistry ", leading to the coiiception of atonis : next come the investigations of Ga>--I,ussac, and the niolecular theory, a short chapter ( j pages) on the deteriiiinatioii of molecularweiglits: iii solution, then atomic heat. isoniorphisiii, and filially the periodic law. \vhat is logically the secoiirl division of the work is iiitroducetl by a long chapter on valency, in \\-hich the evolution of that coiiception is traced to its present state : a definition of the ' constitution or structure of cliernical cotnpounds ' folloivs. and the rerriaiiiing two hundred pages 1 except thirteen on chemical affinity) are devcted to full discussions of the constitution of various classes of compounds, organic ancl inorganic. and to the connection between chemical constitution and properties of compounds. A Treatise on Magnetism and Electricity. Iiz t x f o ivi-I I I I L E S , 1701. I. 1'6 X 23 c i i i ; pfl. nitd 479. A\7ew Yo)% : The lJlac~)ii/lcrr~ Co.. 1S97. Price : $4.50. --The subjects of the chapters are : permanent mag- iietisni ; magnetic ititeiisi1.y and niagnetic induction ; terrestrial tnagiietisrri : tnagnetisni of an iron ship and conipensation of the compass ; elementary phenomena and theory of electrostatics ; steady flow of electricity in linear coiicluctors : general dynaniic:tl theory : motion of a fluid ; elementary facts and theory of electromagnetisrri ; induction of currents ; dytianiical theory of current induction : general electrotnagtietic theory ; the voltaic cell : thertiioelectricity. .it first sight it ~vould seem as if this book coiitainecl little that woulrl interest the chemist : but i t closer inspection shows the incorrectness of such a view. The chapters on tlie elementary phenomena and theory of electrostatics, on the elementary facts :ind theory of electroniagnetisni. and on iiitluction of currents contain many things that the chemist sliould kiiow ; while the chapters on the steady flo\\. of electricity in linear conductors, 0x1 thermoeiectricity, and on the voltaic cell, contain niatter that is quite as important to the chemist as to the physicist. The chapter 011 the voltaic cell is oiie of the poorest in the hook : but the reason for this appears to he that tlie more interesting phenomena are to he treated in the second volume. The general style of the hook is so good that one is grieved to read, even in a quotation, ahout " the energy expatided in algebraically geiierating reversible heat." The typograpliical errors are few in number and consist chiefly of dropped letters. 1ViIdev D . Bancvoff Practical Exercises in Electrochemistry. B,v F. Oetfel. Audhorized tvn?2s-Intiotz by E&nr 1". Shzith.. Philnde/phin : P. 1V. Ltrsh ,lZillev By A?tdvcw GI-ny.