244 



NATURE 



{July II, 1889 



together. No other of equal originality is equally easy 

 to understand. The intellectual pleasure which is com- 

 pounded of mathematical exertion and the interest in 

 human affairs is here enjoyed must purely. F. Y. E. 



PROFESSOR VON " CRANK." 



Richtigstellung der in bisheriger Fassufig unriclitigeti 

 Mechanischen Wdrmethcorie unci Grundziige einer 

 allgemeinett Theorie der Aetherbewegungen. Von 

 Albert R. von Miller-Hauenfels, Professor a. D. in 

 Graz. Pp. 256. (Wien : Manz'sche k.k. Hof-Verlags- 

 und Universitats-Buchhandlung, 1889.) 



IT is quite refreshing to come across a real " crank " 

 among the sober Germans. As might be expected, 

 there is a good deal of irregular metaphysics involved in the 

 lucubrations of a German " crank." One would not, how- 

 ever, expect an entire ignorance of the first principles of 

 the mathematics involved. The author of this hardly 

 sufficiently ingenious to be even curious work begins by 

 objecting to the well-known thermodynamic equation for 

 perfect gases — 



dv „ pv 



W-c)=P 



dt 



R 



T' 



because, forsooth, it is not identical with the general 

 dififerential equation — 



forgetting that the definition of C, as he himself gives it, 

 assumes that, in the first equation, p is constant. In 

 order to escape this invented difficulty, he loads himself 

 with an equation — ■ 



]^ = ]cdt^vdp-irpdv, 



which involves the remarkable result that the heat required 

 to warm a gas at constant volume is JQ = ]cdt + vdp, 

 while by definition it is = ]cdt. It is not necessary to 

 remark that the author carefully neglects to draw this 

 conclusion. His equation is founded on the interesting 

 principle that, when any event produces two different 

 effects on the same organ of sense, each effect must be 

 due to a separate flow of energy. When a mass of gas 

 is warmed at constant volume, and one resists its expan- 

 sion, one feels two effects with the same organ of sense : 

 (i) the increase of pressure, and (2) the increase of tem- 

 perature ; and it is argued that each must be due to a 

 separate flow of energy. This interesting principle leads 

 to the startling conclusion that the heat required to 

 change a body from one state to another, is independent 

 of the states through which the body passes, and depends 

 only on the initial and final states ; and this startling 

 oonclusion involves the equally startling inference that 

 the internal energy of a body is a function of the states it 

 has passed through. It would be very interesting to 

 study the difference between water that had frequently 

 passed through some cyclic process, and water which 

 had not : no chemist has yet detected the difference. 



It would be multiplying words without wisdom to go 

 through the elaborate bolstering of hypothesis by assump- 

 tion and unreason required to deduce any semblance 

 to fact from these beginnings. It may however, be 



worth while to notice something in the second part of 

 this work on the nature of the ether. It is assumed that 

 Fresnel has conclusively proved that an ether consisting 

 of molecules which. repel one another would transmit 

 transverse vibrations like light ; and, in order to turn the 

 difficulty of the existence of longitudinal vibrations to 

 useful account, it is assumed that these latter exist and 

 are heat. It is hardly necessary to investigate a theory 

 of electric and magnetic forces founded upon such an 

 ether, and upon some curious ideas as to forces flowing 

 from place to place. 



And what is the use of spending time looking into such 

 a work as this ? It is by studying extraordinary and 

 startling departures from reason, and not the ordinary and 

 familiar ones, that we learn the causes of our aberrations 

 and how to avoid them. It is the same unreasoning pre- 

 judice for " I can hardly believe it otherwise," the same 

 neglect to study the meanings of symbols, whether words or 

 letters, the same satisfaction with a theory that leads to 

 some true conclusions, which bristle upon every page of this 

 book, and which are some of the most important factors 

 in the prejudice that ignores the necessity for verification, 

 the muddle-headedness that is content with vague notions, 

 the clinging to an incomplete hypothesis that stands in 

 the way of a true theory, all and each of which are in all 

 and each of us such bars to progress. If the study of 

 Prof. Miller-Hauenfels' errors leads to even a state of 

 preparedness to look out for similar errors in our own 

 work, the study will have been fruitful. G. F. F. G. 



OUR BOOK SHELF. 



Traite Encyclopedique de Photogra-phie. By Charles 

 Fabre. Vol. I., Part I. (Paris": Gauthier-Villars, 

 1889.) 



This is the first part of an encyclopaedic work on the 

 history and development of photographic methods. Its 

 general object is to set forth, not only full particulars of 

 the methods now in actual use, but also a complete story 

 of the gradual improvements which have led up to them. 

 There is little doubt that the rapid progress which has 

 been made in photography has been largely due to the 

 fact that the whole subject is so new, that every in- 

 vestigator who sets himself to work soon becomes 

 familiar with what has gone before, and is thus in a 

 position to consider what further advances are possible. 

 It is certainly not too much to expect that such a work 

 as is contemplated by M. Fabre will do a great deal 

 towards simplifying the acquirement of this knowledge. 



It is proposed to issue the work in twenty monthly 

 parts, of which five parts will constitute a volume. The 

 first volume will treat more particularly of the general 

 history of photography and photographic apparatus, 

 special attention being given to the subject of lenses. 

 The second volume will deal with the production of 

 negatives, and the third with positives of every de- 

 scription. The fourth volume will first treat of the 

 methods of enlargement, and then of photographic 

 chemistry and theories of the formation of photographic 

 images. This comprehensive scheme, if well followed 

 out, as no doubt it will be, if we may judge by the excel- 

 lence of the first part, will obviously constitute a valuable 

 addition to photographic literature. 



In the first part the whole subject of lenses is con- 

 sidered, from the chemical composition of the various 

 kinds of glass employed in their construction to the various 

 combinations now used. Spherical aberration, distortion, 



