February 27, 1908] 



NA TURE 



389 



labour-saving device for the dairyman it has been 

 ranked with the separator. 



Certain statements will want correction in a future 

 edition. We are told, for instance, that " the covering 

 of land in summer prevents the temperature from 

 rising so high as to destroy the organisms of the 

 soil." E. J. R. 



OUR BOOK SHELF. 

 Astronoinischer Jahresbericht, Vol. viii. Die Liter- 



atur des jahres igo6. By A. Berbcrich. Pp. 



xxxvi + 671. (Berlin : Georg Reimer, 1907.) Price 



21 marks. 

 Astronomers are fortunate in the matter of having 

 their literature catalogued, for, in addition to the 

 volume published by the Royal Society for the Inter- 

 national Council, we have this very excellent annual, 

 instituted by the late Dr. Walter F. Wislicenus, which 

 has now reached its eighth volume. 



The contents of the present issue deal with the 

 literature of the year 1906, and it only requires a 

 cursory glance to indicate how important it is that 

 such a catalogue is in existence, considering tlie 

 great mass of work that is being turned out every 

 year and published, not only in all sorts of journals, 

 but in various languages. 



The very arduous task of collating and cataloguing is 

 now annually being successfully accomplished by Dr. 

 Berbtrich and his co-workers, and an important 

 feature about the publication is its early issue. 



In the present volume, which contains no less than 

 ig6i separate brief abstracts of published papers, 

 accompanied by a complete name-index, some minor 

 changes have been made. 



Thus all references to publications with regard to 

 minor planets are brought together under one section 

 number, and the tabular statement of their observation 

 is here omitted, as it appears in full in the Berlin 

 Astronomical Year-book. 



The literature relating to comets is now divided 

 between two sections, while one section includes the 

 whole of meteor-astronomy. 



In spite of the above and other alterations, the 

 volume is not reduced in size, for longer abstracts 

 are given of works of greater importance. 



The value of this publication to astronomers cannot 

 be overestimated, and it behoves everyone interested 

 in this science to support it, so that the continuation 

 of future issues may be assured. 



Lehrbitch der theoretischen Elektrochemie auf thernio- 

 dynamischer Grundlage. By J. J. van Laar. 

 Pp. xii + 307. (Leipzig: W. Engelmann ; Amster- 

 dam : S. L. van Looy, 1907.) Price 6 marks. 

 The present volume differs greatly in character from 

 those to which w-e are accustomed from the pen of 

 Dr. van Laar. His " Thermodynamik in der Chemie " 

 and his " Lehrbuch der mathematischen Chemie " are 

 so formal in their nature, so mathematical in their 

 dress, and so slightly connected with the facts of 

 observation, that the majority of chemists can have 

 derived little benefit from them, excellent though they 

 may be of their kind. Here the author adopts a 

 different method ; the mathematical deductions have 

 the clearness and conciseness which might be ex- 

 pected, but everywhere the experimental data are 

 brought into the foreground, so that the electrochemist 

 with a modest mathematical equipment may hope to 

 gain a clear view of the thermodynamical theory of 

 his science. 



The book is divided into twelve chapters, of which 

 the first deals with electrical units, chapters ii.-iv. 



NO. 2000, VOL. yy] 



with conductivity, chapter v. with diffusion, chapters 

 vi.-x. with electromotive force, chapter xi. with 

 polarisation, and chapter xii. with capillary electric 

 phenomena. 



A good account of the work of Kohlrausch is given 

 in chapter iii., and the recent researches of Walden 

 and others on the conductivity of non-aqueous solu- 

 tions, and of Lorenz on fused electrolytes, are well 

 summarised in chapter iv. Chapter vii., on the par- 

 tition equilibrium of electrolytes, contains much that 

 is novel. 



Altogether it may be said that the book is readable, 

 original, and suggestive. 



Coal. By James Tonge. Pp. vii + 275. (London: 

 .■\rchibald Constable and Co., Ltd., 1907.) Price 

 bs. net. 

 The author recently published an excellent little work 

 on coal-mining for the use of students. It is dis- 

 appointing, therefore, to find that in writing a book 

 on coal for the general reader he has been less suc- 

 cessful. The work appears to have been hastily com- 

 piled, and the proofs carelessly revised. For example, 

 the Ruhr appears as " Rurh," Courrieres as " Cour- 

 rieries," Anzin as " Auzin," Resicza as " Kesicza," 

 and Karwin as " Kirwin." 



There is a useful chapter on the preparation of coal 

 for the market ; and the chapter on the botany of the 

 Coal-measure plants is excellent, though somewhat 

 technical for the general reader. Both these chapters 

 are admirably illustrated. The chapters on the British 

 and foreign coalfields, on the valuation and uses of 

 coal, on the production of heat from coal, and on the 

 waste of coal, contain, however, little that is not better 

 set forth in the report of the Royal Commission on 

 Coal Supplies, in the valuable digest of that report 

 published by the Colliery Guardian, in Prof. Flux's 

 revised edition of Jevons's work, or in other works 

 dealing with coal. Of such works many have 

 recently been published, for we cannot agree with the 

 author that " it is now many years since a work on 

 coal was presented to the public." 



LETTERS TO THE EDITOR. 



IThe Editor does not hold himself responsible for opinions 

 expressed by his correspondents. Neither can he undertake 

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

 manuscripts intended for this or any other part 0/ Nature. 

 No notice is taken of anonymous communications.] 



The Speed of Racing Animals. 



In Nature, March 14, 1907, p. 463, there is an article 

 giving 'the results obtained by Prof. Kennelly, of Harvard, 

 from an examination of racing records. There is no harm 

 in again directing the attention of your readers to these 

 results. Prof. Kennelly 's paper was sent July 6, 1906, to 

 the American .'\cademy of Arts and Sciences, and published 

 in the Proceedings in December, 1906. It is entitled " An 

 Approximate Law of Fatigue in the Speeds of Racing 

 Animals." His general result is given in a question set 

 by me in an examination in practical mathematics, 

 January, 1907. Here is the question : — 



If t seconds is the record time of a race of y yards ; the 

 law t = cy"- seems to be wonderfully true for all record 

 races of men and animals excepting men on bicycles ; n is 

 the same number in all cases, c has a special value in 

 each case, men walking, running, skating, swimming, or 

 rowing ; horses trotting or galloping or pacing. 



(i) For any particular kind of race it is found that when 

 y is increased by 100 per cent., t is increased by 118 per 

 cent. ; find n. 



(2) For men running, when y = 6oo, i is 71 ; find c in 

 the above formula. Express i, the average speed of each 

 race, in terms of y. 



(i,) Assume that an animal has a certain amount of 

 endurance E which is exhausted at a uniform rate during 



