October 4, 1906] 



NA TURE 



su'^^g'cstions as to their improvement. The account of 

 I he British and Irish rivers is rather depressing read- 

 ing. .Mmost everywhere, save in a few favoured 

 counties, there is th(^ tale of pollution. We agree 

 with Mr. Hodgson that this is preventable. The crude 

 by-products of various manufactures need never be 

 turned into fishing rivers— such a thing, for instance, 

 as the reckless discharge of sawdust into a stream, 

 and the consequent destruction of hosts of trout, 

 ought certainly not to be permitted. With modern 

 methods of septic purification it is a scandal that 

 salmon rivers and streams should still be the reposi- 

 tories of crude sewage; but local sanitary authorities 

 are ditHcult to iTiove, and so far as the prevention of 

 the pollution of rivers is concerned the law " is a 



The book is excellently printed and illustrated. 

 Particular praise should be given to the series of 

 seven plates at the be.ginning of the volume illus- 

 trating eighty typical salmon flies. The colouring 

 and printing of these plates leave nothing to be 

 desired. -Altogether Mr. Hodgson's book should be 

 .1 very welcome addition to the sportsinan's library. 



In " Dry Fly Fishing " Mr. F. G. Shaw makes a 

 creditable attempt to make clear that which he terms 

 the " science " of trout fishing. Chapters i. and ii. 

 give directions how, when, and where to cast a trout 

 lly. Chapter iii. deals with the selection of the fly, 

 and includes a discussion of the range of vision of 

 the fish. Chapter iv. gives a useful account of sonif 

 aspects of pisciculture, and chapter v., " The necessi- 

 ties of the trout fisherman," is devoted to a consider- 

 ation of the " gear " necessary for the craft. The 

 boolv is abundantly illustrated. If the niceties of 

 trout fishing can be taught bv means of diagrams and 

 practical directions, then Mr. Shaw's book ought to 

 be very useful ; but, as he says himself, " It is of no 

 use to read books in order to determine your actions 

 when actually fishing. Coinmon sense is the most 

 valuable guide." Nevertheless, the experience of 

 others is always interesting, and no doubt the tvro, 

 and even those of greater knowledge, will learn 

 much from this work. J. J. 



PROF. LVDWIG BOLTZMANN. 



ONLY two years ago Dr. Ludwig Boltzmann, pro-- 

 fessor of physics in the University of Vienna, 

 celebrated his sixtieth birthday. On that occasion a 

 " Festschrift " was presented to him containing papers 

 by about 125 physicists from all parts of the world. 

 The announcement of Prof. Boltzmann "s death, which 

 was reported in the London papers of September 8, 

 will be received with regret, not onlv by physicists of 

 repute, but by every student who has attempted to 

 gain an insight into the mysteries of molecular 

 plivsics. 



Ludwig Boltzmann was born on February 20, 1844. 

 Before he was twenty-two years old, on February 8, 

 i8{>6, he read a paper before the .Academv of .Sciences 

 of Vienna entitled " Leber die mechanische Bedeu- 

 tung des zweiten Hauptsatzes der Warmetheorie." 

 The opening sentences of the paper may be freely 

 translated as follows : — 



" The identity of the First Law of Thermodynamics 

 with the principle of vis tnva has long been known, 

 on the other hand the Second Law occupies a 

 peculiarly exceptional position, and its proof is based 

 on methods which are not only uncertain here and 

 there, but are in no case obvious. The object of this 

 paper is to furnish a purely analytical and perfectly 

 general proof of the Second Law of Thermodynamics, 

 as well as to investigate the corresponding principle 

 in Mechanics." 



Little did the young Boltzmann imagine that th. 

 task he had thus set before himself would occupy his 

 whole lifetime. 



.-\ year later, after having obtained the doctorate, 

 and having been appointed assistant in the physical 

 institute at Vienna, we find him writing on the 

 number of atoms in a gas molecule and the internal 

 work of gases. 



In 186S he published his first important paper on 

 the law of partition of energy under the title of 

 " Studien iiber das Gleichgcwicht der lebendigen 

 Kraft zwischen bewegten materiellen Punkte." The 

 problem had been previously attacked by Maxwell, 

 but Boltzmann soon found difficulties and objections 

 arising out of Maxwell's treatment, and it was one 

 of the objects of the paper to place the theory on a 

 more satisfactory basis. .A second paper on the same 

 subject (" U'eitere .Studien ") was published in 1S72, 

 and in it the important theorem now known as Boltz- 

 mann's " minimum theorem " or the " H-theorem " 

 first saw the light. That this theorem is not indepen- 

 dent of assumed hypotheses has been amply shown by 

 discussions in N.\TiJr<K and elsewhere in which Watson, 

 Burburv, and other physicists took part early in the 

 'nineties ; but, granting these premises, it is proved 

 that in a system of molecu'es a tendency exists to 

 assume an equilibrium distribution of energy analo- 

 gous to the tendency to heat equilibrium in a material 

 gas. It was not until 1892 that Boltzmann published 

 a third part to his "Studien." In it he deals with 

 difficulties that had been raised in the discussion re- 

 ferred to in connection with the assumption that the 

 kinetic energy of the system could be reduced to a 

 sum of squares, and he also examines certain test 

 cases of the kinetic theory proposed by Lord 

 Kelvin. 



In 187; Boltzmann. then a corresponding member 

 of the Vienna Academy of Sciences, treated _ the 

 problem for the case of a system of molecules in a 

 field of external force. 



From A'ienna Boltzmann went to Graz, where he 

 \vas appointed professor in the university. .After 

 £ft>lng there he wrote, in 1876, a paper on the integra- 

 tion of the equations of molecular motion, and several 

 oth'T minor papers on the kinetic theory. A fresh 

 line was started in 1877, although the underlying- 

 idea had been suffp-ested bv Boltzmann in 1871. and 

 employed by Dr. Oskar Emil Meyer in his book of 

 1877. ' This was the application of the theory of 

 probability to the problem of enerpy-nartition. The 

 method of treatment adopted is highly instructive; 

 Boltzmann starts with considering a system of mole- 

 cules the energy of each of which can only have one 

 or other of a'series of discrete values— a series of 

 counters marked i, 2, -; . . . might be used in illus- 

 tration—and he investigates the most probable dis- 

 tribution of energy for a number of them drawn at 

 random. From this simple case he is led by gradual 

 stae-es to the more complicated case of a gas the 

 molecular state of which is specified by generalised 

 coordinates. 



In 1S80 to 1882 Boltzmann nubllshed long and 

 important papers on viscosity .-rnd diffusion of gases, 

 in which the consequences of Maxwell's assumption 

 of the " inverse fifth " law of intermolecular force 

 were fully discussed. In 1884 he was evidently 

 attracted bv Helmholtz's work on monocyclic systems, 

 and lost no time in aoplyintr the method to the 

 kinetic theory. In this connection the possibility of 

 building un statistically monocyclic systems was con- 

 sidered." But a further application suegested itself in 

 the possibility of representing thermodynamic and 

 '^ther phenomena bv mean« of mochnnical models. 

 In his " Vorlcsungen iiber Maxwell's Theorie," pub- 



NO. 1927, VOL. 74] 



