NATURE 



545 



THURSDAY, OCTOBER 5, 1882 



FLUIDS 

 Experimental Researches into the Properties and Motions 

 of Fluids with Theoretical Deductions therefrom. By 

 W. F. Stanley. (London: E. and F. N. Spon, 1882.) 

 "THE aim and general scope of this work is well 

 -*■ described in its modest and explicit preface. It is 

 essentially a tentative and qualitative treatise, the author 

 expressing a wish in his preface that some highly educated 

 mathematician who may care to follow him, will clothe 

 with his skill the rude, but as he believes, natural under- 

 lying forms he has brought in some cases to light. 

 Modesty such as this, undoubtedly tends to disarm criti- 

 cism, but after a careful perusal of the work, we cannot 

 help cherishing a sincere regret that the author does not 

 himself happen to be the much desired mathematician. 

 We feel certain that if this had been the case, many 

 mistakes would have been avoided, much speculation 

 curtailed, and the value of the work considerably enhanced. 

 Thus while the author admits that " the eighth chapter is 

 very incomplete on certain points for want of suni.ient 

 research into the works of others and more experiment," 

 we find the work characterised throughout by a lack of 

 the same knowledge of what is already known, or has 

 been done by others. 



Too often also the deductions appear to have been 

 preconceived, and the experiments from which they are 

 supposed to follow are either too rough, or of too special 

 a nature. 



As the author speaks disparagingly of his own educa- 

 tional acquirements, it would be unfair perhaps to criticise 

 too harshly a literary style, which certainly detracts very 

 much from the pleasure or comfort of studying his work. 

 He might, however, have tried to be a little more clear, 

 and somewhat less pedantic in the construction of his 

 sentences. Almost every idea has to be disinterred from 

 a heap of polysyllabic adjectives and adverbs, which most 

 effectually obscure its meaning, while very often we meet 

 with paragraphs of, at any rate at first sight, a most 

 incomprehensible character. Such as the following : — 

 " Such equilibrium acts as a condensation upon the 

 surface of a liquid, thereby increasing the molecular 

 surface density,'' or "the area of efflux of the liquid will 

 be the mean of the directive impulses of vertical and 

 horizontal pressures." Elsewhere he speaks of " a narrow 

 vacuous plane " and " motive quiescence." 



On the other hand there is much that is novel and 

 worth perusal in the book, more especially in Chapters 

 IV., V., VI., and VII., and in Section III. on waves. 



One very prominent fault which we notice all through 

 the work, is the almost entire absence of any distinction 

 between the physical properties of compressible and in- 

 compressible fluids. The words fluid and liquid are used 

 quite indifferently, and whatever principles the author 

 deduces for water, are immediately and without trial 

 assumed to be true for air and gases, and vice versa. 

 Again, the experiments which are mostly of a very simple 

 and rudimentary character, are not sufficiently diffe- 

 rential. Thus in experiments on liquids, water alone is 

 employed, and in like manner air is the sole representative 

 Vol. xxvi. — No. 675 



of the gaseous state, though in a work dealing with fluids 

 generally, one might have expected to hear something at 

 least of the properties of all the more easily procurable 

 gases and liquids. 



The first three chapters deal with the theory of the 

 constitution and motive properties of fluids, and are, as 

 the author admits in his preface, " speculative and even 

 in parts hypothetical." In opposition to Clerk Maxwell 

 and others, he holds that " Fluids are composed of static 

 atoms, infinitely tough and elastic, their fluidity depending 

 on the presence of gases or liquid vapours held by attrac- 

 tive forces upon the molecular surface and intruded inter- 

 molecularly, the surrounding envelope of gas acting as a 

 lubricant to the motions of the molecule composing the 

 liquid proper." 



This system of gaseous atmospheres surrounding the 

 molecules is supposed to extend to all matter, and ex- 

 pansions by heat forces to vary as the powers of evapora- 

 tion of the separate molecules. From this point of view 

 the author attacks the theory which has been considered 

 to satisfactorily explain the phenomena observed by Mr. 

 Crookes in high vacua. He maintains that such pheno- 

 mena are not due to the projection of the molecules of 

 the residual gas, but to convection currents of gas formed 

 of metallic matter composing the negative pole. He 

 does not, however, attempt to give any adequate explana- 

 tion of several of the accompanying appearances observed, 

 such as molecular shadows, and phosphorescence, the 

 circumstances attending which, so strongly favour the 

 theory of the rectilinear propagation of the free molecules 

 of residual gas, which depends, as Mr. Tolver Preston has 

 lately suggested, on " the relative dimensions of the con- 

 taining vessel to the mean path of the molecules," and 

 are so completely inexplicable by the physical properties 

 of any ordinary convection current. 



In his preface, the author says he ventures to differ 

 from the generally accepted theory of tensile surfaces 

 for liquids, and prefers to consider them extensile. In 

 Chap. II. he thus defines these words: — 



"By tensile I intend a disposition of the parts of a 

 system of matter to draw themselves together as a 

 stretched drumskin does. By extensile I intend the 

 reverse of this, or the disposition of the parts of a system 

 of matter to separate, and thereby to engender external 

 pressures." 



He then proceeds to show how, according to his theory 

 of the constitution of liquids, the surface (except in the 

 case of free films) has a tendency to extend by virtue of 

 surface condensation arising from the cohesive force 

 between the superficial molecules. 



We fail, however, to see how this assumed surface 

 condensation gives rise to extensibility, since no force 

 other than a strictly lateral one can act at the surface of 

 a liquid without being equally felt all through it, while it 

 would obviously be arguing in a circle to say that lateral 

 attraction of superficial molecules produced lateral ex- 

 tension of the surface. 



Moreover the author assumes that a tensile surface is 

 one which is so stretched already, that it would give way 

 under any additional pressure, while extensile is used to 

 mean not so much disposition to extend, as capability of 

 stretching. 

 Thus the familiar experiment of the needle floating on 



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