NATURE 



521 



THURSDAY, SEPTEMBER 28, iJ 



MODERN PHYSICS 

 The Concepts and Theories of Modern Physics. By J. B. 

 Stallo. (London : Kegan Paul, Trench, and Co., 

 1882.) 



7 "'HIS is, in many respects, a curious work. It shows 

 very extensive reading, as well as much patient 

 thought, on the part of its author ; and is, throughout, emi- 

 nently " readable,'' although somewhat disfigured by the 

 use of strange and uncommon words, such as "question- 

 ability," "irrecusable," "luminar," "consiliences," &c, 

 and even of words apparently made for the occasion. 

 With engaging frankness, the author tells us in the Pre- 

 face that a previous work of his was written when he 



" was under the spell of Hegel's ontological reveries : — 

 at a time when I was barely of age and still seriously af- 

 fected with the metaphysical malady which seems to be 

 one of the unavoidable disorders of intellectual infancy. 

 The labour expended in writing it was not, perhaps, 

 wholly wasted, and there are things in it of which I am 

 not ashamed, even at this day ; but I sincerely regret its 

 publication, which is in some degree atoned for, I hope, 

 by the contents of the present volume.'' 



His recovery from this direful malady has been un- 

 usually complete ; but the sequelae are still of a somewhat 

 distressing character, for the work is "designed as a 

 contribution, not to physics, nor, certainly, to metaphysics, 

 but to the theory of cognition." 



Having been himself at one time enchanted in the 

 Circean sty of metaphysics, the author now sees the evil 

 thing everywhere rampant, and specially in scientific 

 writings. With a subtlety which is occasionally almost 

 admirable, he seems to endeavour, under cover of perfect 

 candour and confidence along with intense zeal for the 

 interests of science, to insinuate into the reader's mind 

 doubts of the validity of some of the most fundamental 

 of scientific hypotheses and reasonings. We rise from a 

 perusal of his volume with a feeling of dawning doubt 

 which happily vanishes the moment we attempt to find a 

 justification for it. We can, however, fancy some ardent 

 student, unversed in laboratory work and with no great 

 knowledge of physical principles, falling an easy victim to 

 the doubts here suggested ; the author all the while 

 smiling grimly to himself as did the spirit of negation 

 when his admiring victim exclaimed — 

 .... mir wird so dumm 

 Als geh' mir ein Miihlrad im Ivopf herum. 



This insidious weakening of the student's faith in prin- 

 ciples and methods is perhaps even more dangerous to 

 scientific progress than w-hat the author in his Preface 

 speaks of as 



" the shallow and sciolistic materialism — I allude, of 

 course, not to its supposed ethical but to its purelv intel- 

 lectual aspects — which for a time threatened to blight the 

 soil and poison the atmosphere even of the old highlands 

 of thought on the continent of Europe, [and which] claims 

 to be a presentation of conclusions from the facts and 

 principles established in the several departments of 

 physical science." 



The author is seen at his best and also at his worst 

 in the Chapters on the " Kinetic Theory of Gases ; " and 

 the whole character and tendencies of his work will be 

 Vol. xxvi. — No. 674 



easily gathered by any one who carefully peruses the 

 following extracts from that chapter. To these we need 

 scarcely add a word of comment : — 



" It thus appears that the pre-supposition of absolute 

 elasticity in the solids, whose aggregate is said to consti- 

 tute a gas, is a flagrant violation of the first condition of 

 the validity of an hypothesis — the condition which requires 

 a reduction of the nui.ber of unrelated elements in the 

 fact to be explained, and therefore forbids a mere repro- 

 duction of this fact in the form of an assumption, a fortiori 

 a substitution of several arbitrary assumptions for one 

 fict. Manifestly the explanation offered by the kinetic 

 hypothesis, in so far as its second assumption lands us in 

 the very phenomenon from which it starts, the phenome- 

 non of resilience, is (like the explanation of impenetra- 

 bility, or of the combination of elements in definite pro- 

 portions by the atomic theory) simply the illustration of 

 idem per idem, and the very reverse of a scientific proce- 

 dure. It is a mere versatio in loco — movement without 

 progress. It is utterly \ain ; or rather, inasmuch as it 

 complicates the phenomenon which it professes to expli- 

 cate, it is worse than vain : — a complete inversion of the 

 order of intelligence, a resolution of identity into differ- 

 ence, a dispersion of the One into the Many, an unravelling 

 of the Simple into the Complex, an interpretation of the 

 Known in terms of the Unknown, an elucidation of the 

 Evident by the Mysterious, a reduction of an ostensible 

 and real fact to a baseless and shadowy phantom." . . . 



" It were work of supererogation to review in detail the 

 logical and mathematical methods by which it is attempted, 

 from an hypothesis resting on such foundations, to deduce 

 formula; corresponding to the facts of experience. I may- 

 be permitted to say, however, that the methods of deduc- 

 tion are only less extraordinary than the premisses. To 

 account for the laws of Boyle and Charles, resort is had 

 to the calculus of probabilities, or, as Maxwell terms it, the 

 method of statistics. It is alleged that, although the indi- 

 vidual molecules move with unequal velocities, either be- 

 cause the velocities were originally unequal, or because 

 they have become unequal in consequence of the encoun- 

 ters between them, nevertheless, there will be an average 

 of all the velocities belonging to the molecules of a sys- 

 tem (i.e. of a gaseous body) which Maxwell calls the 

 'velocity of mean square.' The pressure, on this sup- 

 position, is proportional to a product of the square of this 

 average velocity into the number of the molecules multi- 

 plied by the mass of each molecule. The product of the 

 number of molecules into the mass of each molecule is 

 then replaced by the density — in other words, the whole 

 molecular assumption is, for the nonce, abandoned — and 

 the velocity is eliminated as representing the tempera- 

 ture ; it follows, of course, that the pressure is propor- 

 tional to the density." 



" Similar procedures lead to the law of Charles and the 

 Maw' of Avogadro (according to which the number of 

 molecules in any two equal volumes of gases of whatever 

 kind is the same at the same temperatures and pressures 

 — a law which is itself a mere hypothesis). It is claimed, 

 on statistical grounds again, that not only the average 

 velocity of a number of molecules in a given gaseous body 

 is the same, but that ' if two sets of molecules, whose 

 mass is different, are in motion in the same vessel, 

 they will, by their encounters, exchange energy with each 

 other till the average kinetic energy of a single molecule 

 of either set is the same.' " 



" 'This,' says Maxwell, 'follows from the same investi- 

 gation which determines the law of distribution of veloci- 

 ties in a single set of molecules.' All this being granted, 

 the law of Charles and the law of Avogadro (called by 

 Maxwell the law of Gay-Lussac) are readily derived. And 

 at the end of these devious courses of deduction Maxwell 

 adds a disquisition on the properties of the molecules, in 

 which he claims to have made it evident that the mole- 



