'34 



NATURE 



[April io, 1913 



made to furnish theoretical explanations of the 

 various analytical reactions. A few practical de- 

 tails may be quoted as illustrating- modern ten- 

 dencies in laboratory practice. The difficulty of 

 separating nickel and cobalt is overcome by using 

 dimethvlglyoxime to precipitate the former metal, 

 whilst the latter is identified in an ethereal- ex- 

 tract with ammonium thiocyanate. There is a 

 reversion to an old process in the removal of 

 phosphoric acid from the precipitable metals by 

 means of tin and nitric acid. Absolute alcohol is 

 used to remove calcium nitrate from the mixed 

 nitrates of the alkaline earths. G. T. M. 



THE FLOW OF SUBTERRANEAN WATERS. 

 Le Principe du Mouvement des Eaux Souterraines . 



By J. Versluys. Traduit du hollandais par F. 



Dassesse. Pp. 147. (Amsterdam : W. Versluys, 



1912.) Price 7 francs. 



CALCULATIONS concerning- the flow of sub- 

 terranean water have almost invariably 

 hitherto been based upon the classical law of 

 Da rev, published in 1856 — a law which states that 

 the quantity discharged is directly proportional to 

 the head, and inversely proportional to the thick- 

 ness of the stratum traversed. The terms are 

 simple, and, for general purposes, are sufficiently 

 close approximations to the truth. 



It has been demonstrated more than once that 

 the "law" is not absolutely exact, and, in several 

 cases, the divergency from experimental results 

 has been considerable. The law, in fact, has mani- 

 fest limitations. Darcy omits all reference to 

 temperature, and, indeed, it is doubtful whether he 

 was acquainted with the experiments of Poiseuille, 

 although these had been published ten years 

 earlier, in 1846. The results obtained by Poiseuille 

 led that investigator to conclude that the mean 

 velocity of the fluid depended, in part, on its 

 specific gravity and also on the temperature. 



The object of the author of the brochure before 

 us has been to review the situation in the light 

 of recent research, as exemplified by the work of 

 King, Richert, and others. He investigates, in 

 the first instance, the purely theoretical problem 

 of water-flow in its most general form. Then 

 the various numerical results published in the 

 literature of the subject are collated in a form 

 suitable for comparison with the calculated results, 

 and where pronounced divergences occur, obser- 

 vations and explanations are furnished. Finally, 

 for strictly practical purposes, the author gives a 

 series of numerical coefficients for use in cases 

 where merely general approximations will serve. 



The book consists of thirteen chapters and is 

 a most painstaking and valuable compilation of the 

 data at present available on the subject. 

 NO. 2267, VOL. 9lJ. 



OUR BOOKSHELF. 



Das Relativitatspriuzip. Zweite vermehrte 



Auflage. By Dr. M. Laue. Pp. xii + 272. 



(Braunschweig: F. Vieweg und Sohn, 1913.) 



Price 8 marks. 

 The second edition of Prof. M. Laue's book on 

 relativity, though on the same plan as the first 

 edition of 191 1, contains several additions. In 

 chapter ii. a short discussion of a second arrange- 

 ment of the Rontgen-Eichenwald experiments is 

 inserted. The kinematic part of the theory of 

 relativity, chapter iii., shows some slight explana- 

 tory extensions in § 6, and an enlarged discussion 

 of the inadmissibility of propagation of any 

 physical effects with a velocity exceeding that of 

 light (§7). The "cause and effect" point of 

 view here adopted, which leads to a rejection of 

 any hvpervelocity of propagation, seems some- 

 what too narrow. At any rate, it prevented the 

 author from considering the admirable researches 

 on relativistically rigid bodies of M. Born, and 

 especially of Herglotz. In § 8 we remark a fuller 

 exposition and illustration of the notion of " proper 

 time." 



In chapter iv. the vector product of two six- 

 vectors and the four-dimensional " Gauss 

 theorem " are inserted. Chapter v. contains, be- 

 sides a few minor additions, a considerably 

 extended treatment of the theory of the Trouton 

 and Noble experiment, and a much amplified 

 exposition of four-dimensional potential-theory, 

 following the lines of a paper by Sommerfeld. 

 Chap. vi. contains but a few new lines (on pp. 

 148-164), while vii. (Dynamics) contains many 

 changes and ample additions, viz., Minkowski's 

 dynamics of a point-mass, remarks on the founda- 

 tions of the dynamics of continuous bodies (§ 27), 

 and the rotational momentum, with a pair of 

 instructive examples, several minor additions in 

 the following paragraphs, and finally the chief 

 addition to the first edition, namely, relativistic 

 hydrodynamics, giving the general equations of 

 motion, and treating the interesting special case 

 of fluids "of smallest compressibility," both 

 essentially on the lines of a paper by Dr. E. 

 Lamia [Ann. </. Pliys., vol. xxxvii., p. 772, 1912). 



The Dictionary of Entomology. By N. K. Jardine. 



Pp. ix + 259. (London: West, Newman and 



Co.) Price 6s. net. 

 This useful compilation is a glossary of the tech- 

 nical terms used in describing the structure of 

 insects throughout their several stages. Within 

 the limits which the author has imposed on him- 

 self it is likely to be of much service to students 

 of entomology. These limits, it is true, are some- 

 what narrow ; there is no mention of individual 

 species of insects, or of genera or families. The 

 orders, when given, are defined in the briefest 

 possible manner, and frequently there is no 

 indication of the insects comprised in them. The 

 words " Coleoptera " and " Lepidoptera " find a 

 place, but there is no mention of Dermaptera, 

 Odonata, Homoptera, or Heteroptera. Hemiptera 

 and Neuroptera are given, but beyond a bare defini- 



