53S 



NA TURE 



[August io, 1905 



sexes would in all probability be gravely imperilled, 

 and the State would almost certainly have to inter- 

 vene. Ag^ain, while Mr. Wells is doubtless within his 

 rights in scoffing at the racial prejudices of the time, 

 in his scorn of popular notions of " superior " races, 

 " including such types as the Sussex farm labourer, 

 the Bowery tough, the London hooligan, and the 

 Paris apache," and in his contention that " no race 

 is so superior as to be trusted with human charges," 

 his anticipation of wholesale racial fusions seems to 

 involve a serious underestimate of the aesthetic 

 instincts. Lastly, although Mr. Wells has keenly 

 percei\-ed the spiritual value of a temporary retreat 

 from society, it may be doubted whether he does not 

 purchase its advantages at too high a cost. The 

 solitarv voyages of his .Samurai would assuredly lead 

 to a high death-rate among them, and though one 

 type of mind was thereby strengthened, another would 

 be unhinged. The rule, in short, seems too rigid 

 for the varietv, and too cramping for the freedom, of 

 man, both of which Mr. Wells is elsewhere anxious 

 to appreciate. But Mr. Wells, on the whole, shows 

 a wisdom far superior to that of former L'topists in 

 not seeking to construct out of the imperfect 

 materials which alone the actual can furnish a static 

 order which shall be, and if possible remain eternally, 

 perfect. He aims rather at laying down the prin- 

 ciples of an order which shall be capable of pro- 

 gressively growing towards perfection ; and so it may 

 well be that in his ideal society men will be less 

 reluctant than now to learn from experience. 



F. C. S. S. 



TH£i?iUODrA'.4-l//r5. 



Thcrniodynamik. By Dr. W. Voigt. Vol. ii. Pp. 



.xii + 370. (Sammulung Schubert, xlviii.) (Leipzig: 



G. J. Goschen, 1904.) 

 Diagrammes ct Surfaces thermodynamiqiies. By 



J. W. Gibbs. Translated by G. Ray, of Dijon, with 



an introduction by B. Brunhes, of Clermont. 



Pp. 86. (Paris: Gauthier-\"illars, 1903.) 

 'T'HE second vojume of " Thermodynamik " deals 

 essentiallv with applications. It is divided into 

 two parts, devoted to thermochemical changes and 

 thermoelectric changes respectively. Under the first 

 heading are included changes of phase of a single 

 substance, which occupy the first 1(38 pages. In this 

 connection we have sections dealing with \'an der 

 Waals's formula, steam and gas engines, the 

 equilibrium of an atmosphere of water vapour, and 

 the Hertzian adiabatics. The next chapter deals with 

 phases formed of more than one component, the 

 properties of binary mixtures occupying- about 80 

 pages, and those of a system with more than two 

 components being treated subsequently. The part 

 dealing with thermoelectric changes contains a good 

 bit of introductory matter on electrostatics. In the 

 third chapter of this part the properties of black-bodv 

 radiation are discus.scd at much length. 



The subject of thermodynamics can be defined in 

 various ways. In its most restricted sense it deals 

 n.\clusively with the first and second laws and direct 

 NO. 1867, VOL. 72] 



deductions from them, in just the same way that 

 dvnamics deals with direct deductions from the laws 

 of motion. But the name thermodynamics is often 

 used to include all phenomena directly or indirectly 

 associated with heat, and it is in a fairly broad sense 

 in this respect that Dr. Voigt deals with the subject. 

 A good manv of the formulje are based more or less 

 on experiment or reasoning not directly connected 

 with the two laws of thermodynamics. Thus, for 

 e.xample, in the chapter on radiation the only piece 

 of work which can be regarded as thermodynamical 

 in the narrower interpretation is the proof of the 

 equation bv which Stefan's law is deduced from the 

 formulas for radiation pressure. But in addition to 

 this we have here a general discussion of nidiation 

 based on electrodynamical considerations, Wien's 

 law, Planck's law of mixture, and Kirchhoff's 

 theorem. The relation between the black radiation 

 and wave-length is in no way deducible directly from 

 the first and second laws. 



These examples mav be taken as affording some 

 indication of the extended scope of the book. Passing 

 to matters of detail, the author is to be congratulated 

 on the lucid way in which he clears up many points 

 usually regarded as obscure. We may instance the 

 detailed discussion of the thermodynamical potential 

 of a gas-mixture (§ 69), a point which receives scanty 

 attention in many books we have seen. The author's 

 task is made easier by the fact that most of the higher 

 applications of thermodynamics deal with equiUbrium. 

 Now, whether we deduce the conditions of equilibrium 

 from making the available energv a minimum, the 

 entropy a maximum, or by any other equivalent hypo- 

 thesis, the variation of the function selected must in 

 general vanish to the first order, so that the conditions 

 of thermodynamic equilibrium (apart from stability) 

 are deducible from the equations of reversible thermo- 

 dvnamics. Very little is said in this book about 

 irreversible phenomena, and this is perhaps fortunate 

 owing to the great difficulty of dealing with these 

 phenomena in a clear and logical way. The kind of 

 impression which a beginner is likely to form in 

 reading about irreversible thermodynamics ni.-iy be 

 exemplified bv the following three apparently 

 contradictory statements : — " The increase of entropy 

 is tiO/'T. " "The entropy of the universe tends 

 to a maximum." " For a cyclic irreversible cvcle 

 /"jO/T<o." 



It would be hardly an exaggeration to assert that 

 whether any statement in irreversible thermodynamics 

 is right or wrong depends entirely on the wav of 

 looking at it. For example, in § 105 a very little is 

 said about irreversible electric phenomena, which is 

 doubtless correct according to the author's interpret- 

 ation ; but whether this is the best wav of stating the 

 case is necessarily a matter of opinion. 



In connection with the continuity of the liquid and 

 gaseous states, the rule for the horizontal line in the 

 isothermal diagram is deduced from van der Waals's 

 equation (p. 151), and is not treated as a general 

 result. In this method, however, the significance of 

 the rule is somewhat lost. The proper condition that 

 I the rule may hold good is that the liquid and gaseous 



