292 



NATURE 



[July 29, 1897 



1896, and discusses the structure and origin of the Blue 

 Mountains of the colony. Mr. H. C. Russell's paper, in 

 which he shows that the good and bad seasons follow a 

 nineteen years' cycle, appears in the volume, with the 

 discussion which took place upon it. Among other sub- 

 jects and and authors of papers are : The Mika or Kulpi 

 operation of the Australian Aboriginals, by Prof. T. P. 

 Anderson Stuart ; the cellular kite, by Mr. Lawrence 

 Hargrave ; an explanation of the marked difference of 

 the effects produced by subcutaneous and intravenous 

 injection of the venom of Australian snakes, by Dr. C. J. 

 Martin ; recent determinations of the viscosity of water 

 by the efflux method, by Mr. G. H. Knibbs ; the occur- 

 rence of precious stones in New South Wales, and the 

 deposits in which they are found, by the Rev. J. Milne 

 Curran ; the rigorous theory of the determination of the 

 meridian line by altazimuth solar observations, by Mr. 

 G. H. Knibbs ; an address to the engineering section of 

 the Society, by Prof. W. H. Warren ; the machinery em- 

 ployed for artificial refrigeration and ice-making, by Mr. 

 Norman Selfe ; and the present position of the theory of 

 the steam engine, by Mr. S. H. Barraclough. 



Many of the papers are accompanied by plates, that 

 of the Rev. J. M. Curran being particularly well illus- 

 trated. 



L'evolution rdgressivi en biologic et en spciologie. By 

 Jean Demoor, Jean Massart, and Prof. Emile Vander- 

 velde. Pp. 324. (Paris : Felix Alcan, 1897.) 



To show that the laws of biology are followed in the 

 domain of sociology has been attempted by many writers. 

 Unfortunately, bio-sociological subjects are often taken 

 up by naturalists who have little knowledge of social 

 questions, or by sociologists having but a superficial 

 acquaintance with biological realities, the result being 

 unsound conclusions and exaggerated analogies. With 

 the view to see the subject from different aspects, and 

 produce a composite picture in which neither sociology 

 nor biology is given undue prominence, the authors of 

 this book have collaborated in its production. The result 

 is not altogether satisfactory, for the book is really more 

 sociological than biological, and not good at that. The 

 general conclusions which the authors labour to prove 

 are that evolution is at once progressive and retrogressive, 

 that transformations of organs and institutions are always 

 accompanied by retrogression, and that the same laws 

 hold good in the changes of societies as well as organisms ; 

 all the actual forms undergoing transformation, and, in 

 consequence, losing certain parts of their structure. The 

 text of the book is the universal application of the principle 

 of devolution, and in the exposition of it the authors have 

 exercised their ingenuity to the utmost. 



The Geographical Journal. Vol. ix. January to June 



1897. Pp. viii -1- 748. (London : The Royal Geo- 

 graphical Society ; Edward Stanford, 1897.) 



This volume of the Royal Geographical Socxeiy's Journal 

 contains several papers of exceptional interest, among 

 them being Mr. W. L. Sclater's final contribution on the 

 geographical distribution of mammals ; a paper on the 

 formation of sand-dunes, by iMr. Vaughan Cornish ; Sir 

 Martin Conway's account of his Spitsbergen expedition ; 

 two years travel in Uganda, Unyoro, and on the Upper 

 Nile, by Lieut. C. F. S. Vandeleur ; Dr. Nansen's state- 

 ment of the results of his arctic expedition, and his views 

 on the north polar problem ; and a paper by the presi- 

 dent, Sir Clements Markham, on the voyages of John 

 Cabot. In addition to these papers, the monthly record 

 and a number of special articles furnish a store of in- 

 teresting information on geographical progress in its 

 widest sense. Large coloured maps and other illustra- 

 tions accompany the papers, and assist in making the 

 volume valuable. 



NO. 1448, VOL. 56] 



LETTERS TO THE EDITOR. 



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

 pressed 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 of Nature. 

 No notice is taken of anonymous communications. '\ 



The Electro-Chemical Equivalent of Silver. 

 Ln Nature, vol. hi. p. 259, Mr. Griffiths points out that 

 recent comparisons of the values of the mechanical equivalent 

 of heat, obtained by mechanical and electrical methods, suc;ge.st 

 that the adopted value of the equivalent of silver may be in 

 error to the extent of i/iooo. This adopted value rests, I 

 believe, almost entirely upon experiments made by Kohlrausch, 

 and by myself with Mrs. Sidgwick in 1882 ; and the question has 

 been frequently put to me as to the limits within which it is 

 trustworthy. Such questions are more easily asked than 

 answered, and experience shows that estimates of possible error 

 given by experimenters themselves are usually framed in far too 

 sanguine a spirit. 



When our work was undertaken the generally accepted number 

 was •01136, obtained by Kohlrausch in 1873. Mascart had 

 recently given -01124, subsequently corrected to 'oiiise. The 

 uncertainty, therefore, at that time amounted to at least 

 I per cent. The experiments of Mrs. Sidgwick and myself 

 were very carefully conducted, and we certainly hoped to have 

 attained an accuracy of 1/2000. So far as errors that can be 

 eliminated by repetition are concerned, this was doubtless the 

 case, as is proved by an examination of our tabular results. But, 

 as every experimenter knows, or ought to know, this class of 

 errors is not really the most dangerous. Security is only to be 

 obtained by coincidence of numbers derived by different methods 

 and by different individuals. It was, therefore, a great satis- 

 faction to find our number (/"/^Z/. Trans., 1884) (•on 179) con- 

 firmed by that of Kohlrausch (-011183), resulting from experi- 

 ments made at about the same time. 



It would, however, in my opinion, be rash to exclude the 

 question of an error of i/iooo. Indeed, I have more than once 

 publicly expressed surprise at the little attention given to this 

 subject in comparison with that lavished upon the ohm. I do 

 not know of any better method of measuring currents absolutely 

 than that followed in 1882, but an ingenious critic would doubt- 

 less be able to suggest improvements in details. The only thing 

 that has occurred to me is that perhaps sufficient attention was 

 not given to the change in dimensions that must accompany the 

 heating of the suspended coil when conveying the current of ^ 

 ampere. Recent experiments upon the coil (which exists intact) 

 show that, as judged by resistance, the heating effect due to this 

 current is 2^° C. But it does not appear possible that the 

 expansion of mean radius thence arising could be comparable 

 with i/iooo. Rayleigh. 



Terling Place, Witham. 



Acetylene for Military Signalling. 



In conjunction with Captain J. E. S. Moore, I have been 

 making some experiments on the use of acetylene in signalling 

 lamps. We have obtained such good results with the very 

 primitive apparatus at present employed, the light is so brilliant, 

 and the requirements so portable, that it seems well worth con- 

 sidering whether acetylene could not take the place of the lime- 

 light where portability is an object. 



The apparatus consists of a 5-oz. bottle, carrying a two-hole 

 rubber cork ; water drips on to the carbide from a wide glass 

 tube, holding some 2\ oz. , and furnished with a connection of 

 rubber tube and a screw-clamp to act as regulator. The gas 

 escapes from a straight tube to the lamp, being trapped on the 

 way by a wider piece of tube, into which the smaller tubes are 

 corked at either end ; this makes a sufficient condenser for any 

 water vapour. The gas tube enters the lamp through the base, 

 and the gas burns from an ordinary 0000 Bray. The generator, 

 when charged, weighs one pound, and after a couple of minutes, 

 during which time the action is a little irregular, will give a 

 steady light for thirty or forty minutes ; on more than one 

 occasion, indeed, it has run out without the clamp being touched 

 after first adjustment. We find an ordinary lamp small for the 

 heat produced, and have had to rivet the soldered parts ; but 

 increased ventilation would be easy to arrange. Of course for 

 permanent work the generator would have to be arranged in 

 metal ; even then it would probably be the lightest gas-supplying 

 arrangement, for the illumination, yet produced. 



The Laboratory, Felsted, Essex. A. E. Munbv. 



