January 3, 1895] 



NA TURE 



221 



error is once again seen, of mistaking the axis of rotation 

 of the earlh for the plane of the equator ; but such over- 

 sights are easily excused in presence of the collection 

 of a large number of facts, well arranged and tersely 

 expressed. W. E. P. 



The Province of South Australia. By J. D. Woods, 

 J. P. With a Sketch of the Northern Territory, by H.D. 

 Wilson. Pp. 446. (Adelaide : C. E. Bristo'w, 1894.) 



This account of the province of South Australia, from 

 its discovery to the end of 1S92 was, the preface informs 

 us, written under the authority ol the Government of the 

 Colony. It may therefore be taken as an authoritative 

 work of quite a different and a better kind than the many 

 descriptions of Australia that have appeared during the 

 past few years. The physical features, fauna, flora, 

 climate and meteorology are fully de-cribed, and the 

 story of the explorations of the interior of the continent is 

 full of interest. There is a chapter on the agriculture of 

 South Australia, and one on the minerals in which the 

 province is so wonderfully rich. Those familiar with the 

 history of education in .South Australia will remember 

 that prior to 1874 the colony did not possess a university. 

 It was in 1S72 that an endowment of ^20,00'-', given by 

 .Sir W. W. Hughes, was applied to the founding of 

 two professorships — one for classics and comparative 

 philology and literature, and the second for English 

 language and literature and mental and moral philosophy. 

 Science was benefited shortly afterwards by a like 

 donation from Sir Thomas Elder, to found a professor- 

 ship for mathematics and another of natural science. 

 The same benefactor gave ^10,000 for the establishment 

 of a medical chair in 1883, and /J 1000 for evening classes ; 

 and the Hon. J. H. Angas gave /^6ooo for the creation of 

 a chair of chemistry, and ^4000 for the establishment of 

 scholarships and exhibitions. Though the Adelaide 

 University was incorporated in 1874, the present Uni- 

 versity buildings were not opened until 1882. The 

 School of Mines and Industries, as it is officially desig- 

 nated, was opened in 1 889, and has steadily increased in 

 influence and usefulness since then. 



The chapter on the aborigines of South Australia is 

 perhaps the best in the book, and as the author 

 has had more than forty years' experience with the 

 blacks, he writes upon what he is well qualified to de- 

 scribe. Altogether the volume includes much that has 

 not hitherto appeared in print in a collected form, and 

 therefore deserves to rank with the best books on 

 Australia, its people, and its resources. 



Measurement Conversion Diaf^rains. By Robert H. 

 Smith, Professor of Engineering, i\lason College, 

 Birmingham. (London: Charles Griffin and Co., 

 Limited, 1895.) 



The scope of this work is described on the title-page as 

 follows: — ''Forty-three graphic tables or diagrams for 

 the conversion of measurements of different units, com- 

 prising conversions of length, area, volume, weight, 

 stress, density, work ; energy in mechanical, thermal, and 

 electrical units ; hnrse-power, and temperature." Only 

 those who are familiar with graphic statics know what 

 can be done by diagrams, but even they will be astonished 

 at the wide range of conversions covered by Prof. 

 Smith's graphic equivalence plates. The diagrams will 

 principally aid the conversion of English and metric 

 measures, and vice versa, but they also represent the 

 relations between different systems of English, and of 

 French, measurement. We have always been attracted 

 by the method of expressing equivalents by means of 

 squared paper, and Prof. Smith's graphic tables have 

 greatly increased our admiration of it. 



NO. 13 14, VOL. 5 I "I 



LETTERS TO THE EDITOR. 



[ The Editor does not hold himself responsible for opinions ex- 

 pressed by his correspondents. Niither (an he undertake 

 to return, or to correspond with the writers of, rejected 

 manuscripts intended for this or any other part of NATURE. 

 No notice is taken of anonymous communications.^ 



The Kinetic Theory of Gases. 



I DO not feel as if ihose who heard me ask some questions 

 at the British As.<:ociation at Oxford, about the kinetic theory of 

 gases, exactly undfrstood my difficulties. They are those of an 

 oidoriker, and so ihey may be of general interest. As several 

 of ihem have been fairly salisfaciorily answered, it may be 

 worih while stating the present position of such an onlooker as 

 myself. 



In the first place, consider the difficulty as to reversibility 

 and as to the number of possible ways in which a system could 

 be staned on a reverse path so as lo obtain 3. s^ivcn initial state. 

 This is, I think, completely answered in the way Mr. I. armor 

 gives in his letter on p. 152. As well as I can recollect, Mr. 

 Culverwell and I had been mutually sali.sfied by this kind of 

 explanation previous to the meeting at Oxford, and it was 

 not then referred to. 



The questi m of reversibility lately started, as I understand 

 it, has reference to the introduction of the postulate of chance 

 in the deduction of the theorem about H. Mr. Burbury, in 

 his recent letter, has indicated a proof of this theorem, in 

 which he explicitly postulates chances, and so far iusiifies the 

 possibility of proof on these lines. I understand that Mr. 

 Culverwell is so far satisfied, and only asks for more, i.e. an 

 extension of this form of proof to other cases than the simple 

 one of colliding spheres. 



Secondly, as regards the solar system, &c. , I am not yet 

 quite clear why a finite number of particles moving about for an 

 indefinitely long time does not satisfy the conditions of the 

 problem as usually slated, just as well as a larce number of 

 bodies for a short time. As to the necessity for collisions among 

 the parts of a system, I cannot see why the earth, moon, 

 Jupiter, and sun are not to all intents and purpose.? of the 

 generalised coordinates in collision at present and alway- ; and 

 I desired to know why any other kind of collision is required 

 for the applicaiion of the investigation. I think I now see, 

 through conversations with Mr. Culverwell, where the existing 

 investigations may fail to apply to solar systems. I may explain 

 my position as follows. It was always, I knew, postulated 

 that more than two particles should not be in collision at once, 

 and I therefore asked how this could be an essential part of the 

 investigation when applied to the case of air near the earth sub- 

 ject to gravitation. I did not see why the earth was not (so far 

 as the generalised coordinates investigation was concerned) a 

 particle in collision with every particle of the air during every 

 one of their collisions with one amther, and consequently 

 violating the postulate requiring only two particles to be in col- 

 lision simultaneously. I now understand that «hen dealing 

 with gravitation and such like forces, these are supjiosed to be 

 direcied to yf.ivt/ centres, and that in the case of a large particle 

 like the earth this is very nearly true, but that it could not be 

 even approximately true if we had three fairly equal particles 

 acting upon one another simultaneously. This may also explain 

 why the equal partition of energy does not hold in the solar 

 system where the bodies do not act upon one another in pairs, 

 but are all always subject to one another's action. This, 

 as I understand, is also the reason why the direct dis- 

 tance law is not an exception to the equal partition 

 of energy theorem. It also may explain how we can have water 

 and steam in equilibrium with one another, notwithstanding 

 the apparent uniijueness of the Boltzniann-Maxwell .solution. 

 From experience it would seem that when we can extend the in- 

 vestigation to the case of several bodies in simultaneous colli- 

 sion, we shall find that there are three solutions corresponding 

 to the solid, liquid, and gaseous states. At the same lime, 

 some of the very general investigaticus that seem to me, as a 

 physicist, as if they were intended lo apply to complex molecules 

 in collision with one another, and with a partition of energy 

 amongst the atoms, appear lo violaie the postulate of collisions 

 in pairs; for I find it hard to conceive of these molecular systems 

 of atoms as other than systems, the various parts of which are 

 held together by mutual actions, and which must c.nsequently 



