556 



NATURE 



[April i6, 1896 



late the language and the formula of the dualistic system 

 into the language and formuhu current at the present 

 day. The process is simple. It consists in writing down 

 the dualistic formula in equivalents say HO, from this 

 deducing the formula of M. Berthelot, HP2> and then 

 dividing by two the number of equivalents of all elements 

 in the formula not comprised in a table given in the 

 book ; that is, the elements of uneven valency, and so 

 in this case we arrive at the unitary atomic formula 

 H2O. This little book is not wanted in England. It 

 might have been useful thirty years ago, but for very 

 shame it should not have been published now, and ad- 

 dressed to university students by a university professor 

 in the land of Laurent, of Gerhardt, and of Wurtz. 

 French chemistry half a century ago was still in the 

 front rank. For the last generation it has been prac- 

 tically nowhere. France owes a debt to M. Berthelot 

 for his labours of the last forty years, first in the develop- 

 ment of chemical synthesis, and latterly for his store of 

 exact calori metric determinations ; but whatever grati- 

 tude the chemical part of the nation may feel for these 

 substantial labours, the warmth of such feeling must be 

 considerably reduced by the reflection, that chiefly to 

 the obstinacy of M. le Ministre de 1' Instruction publique, 

 an office held for many years by the great chemist, is 

 due the position to which French chemistry has sunk, 

 and from which, spite of the brilliant work of a few men 

 like le Bel, Lecocq de Boisbaudran, and Moissan, it will 

 take the best part of another generation to rise. 



OUR BOOK SHELF. 

 Die Mikroskopische Thienuelt des Siisswassers. Abth. I. 

 Protozoa. Von Dr. Friedrich Blochmann. Zweite 

 Aufl. 4to XV -f- 134 pp., 8 plates, 259 figs. (Hamburg : 

 Lucas Grafe and Sillem, 1895.) 

 It is true that there are many books deaHng with the 

 microscopic fauna of fresh waters, but it is also probably 

 the case that there are many more students and amateurs 

 working more or less seriously at this than at any other 

 branch of microscopic zoology. This is the first section 

 of the second part of Kirchner and Blochmann's " Micro- 

 scopic Fauna and Flora of the Fresh-waters," and the 

 present second edition has been completely reorganised 

 and enlarged. It treats of the Protozoa alone, and dis- 

 cusses them from the systematic point of view. The 

 classification adopted is, in the main, that of Biitschli, but 

 our author agrees with Klebs in the grouping of the 

 Flagellata. We have general accounts of the classes and 

 other divisions, dichotomising tables, and definitions of 

 the genera and species, beginning with Hyalodisciis and 

 Amoeba, and working through to Stylocometes in the 

 Suctorial Infusoria. Volvox and other forms some- 

 times claimed by the botanists are here included in the 

 Flagellata, and of course the Dinoflagellata {Peridinium 

 and Ceratium and their allies) are placed along with the 

 Flagellata in the Mastigophora. The figures on the 

 plates (Werner and Winter) are abundant, and are excel- 

 lently drawn ; a large number of them are tinted so as to 

 show natural colours. Many of them are now very 

 familiar, being taken from the classic works of Biitschli, 

 Leidy, Cienkowsky, Hertwig, Greef, Stein, Klebs and 

 Kent. The last plate gives in outline over forty selected 

 types (the best-known forms) from the various groups of 

 Protozoa, all magnified 100 times so as to show the 

 relative sizes, and enable the student to realise the con- 

 trast between Urotricha and Spirostomum, between 

 Oikomonas and Pelomyxa, and between Actmophrys and 

 Actinosphcerium. W. A. H. 



NO. I 38 I, VOL. 53] 



Manual of Lithology : treating of the Principles of the 



Science, with special reference to Megascopic Analysis. 



By Edward H. Williams, jun. 418 pp. Six plates. 



(New York : Wiley and Sons. London : Chapman 



and Hall, 1895.) 

 In general plan this book differs little from many other 

 text-books on the same subject. The main portion is 

 devoted to the systematic clescription of the different 

 types of rocks belonging to the three groups, primary or 

 igneous, secondary and metamorphic. By way of intro- 

 duction to this part, about a hundred pages are occupied 

 with an account of the principal rock-forming minerals 

 and with definitions of the structures exhibited by rocks ; 

 while at the end is added a short chapter, intended for 

 the engineer, dealing with the economic value of rocks. 

 Throughout the book the subject is treated as far as 

 possible from the macroscopic point of view. In the 

 classification of the igneous rocks, a two-fold division into 

 intrusives and extrusives is adopted. In this system the 

 line of distinction appears to be drawn in the wrong 

 place. The result is that types presenting very similar 

 characters are separated widely from each other ; and 

 owing, it would seem, to the influence of the German 

 school, this separation appears to be effected, in many 

 cases, not so much because the rocks diff'er in mode of 

 origin as because they have been kept apart by German 

 writers who still uphold the criterion of geological age, a 

 method of distinction, however, which we are glad to see 

 the author clearly I'epudiates in the introduction. 



In the description of varieties of the main types many 

 new names, and some old ones which we hoped had 

 become obsolete, will be met with ; so that, in this part of 

 the book, the author's own pages hardly serve to impress 

 upon the reader the truth of the statement made in the 

 introduction that " the tendency of modern rock analysis 

 is toward a simplification of the subject, and the 

 discarding of useless and misleading divisions and 

 names." 



If the book had been kept within narrower limits, we 

 are inclined to think that it would have been more useful 

 to the class of student for whom it is intended, viz. " the 

 beginner in the subject who wishes a thorough knowledge 

 in the megascopic presentation of the subject, in a fuller 

 and more compact arrangement, than can be obtained in 

 geological text-books." G. T. P. 



LETTERS TO THE EDfTOR. 

 [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 atiy other part of Nature. 

 No notice is taken of anonymous communications. ^^ 



The Sacred Tree of Kum-Bum. 



The identification of the Kum-Bum tree with Ligtistrina 

 amurensis (not amurentis) (see p. 534) has already been communi- 

 cated by M. Grigoriev to the Butletin du Mitseuiu d' Hisloire 

 Nattirelle (1896, p. 33). But the Paris botanists appear to 

 consider it doubtful. 



As, however, Ligtistrina is now merged in Syringa, there 

 is a general agreement that the Kum-Bum tree belongs to that 

 genus. We are still of opinion that the authentic leaves brought 

 back by Mr. Rockhill belong to S. villosa. 



Kew, April 10. W. T. Thiselton-Dyer. 



The Rontgen Rays and Optically Active Substances. 

 In an article in Nature (February 27) by Prof. J. J. 

 Thomson, it is suggested that the leakage of electricity through 

 non-conductors under the influence of the Rontgen rays is " due 

 to a kind of electrolysis, the molecule of the non-conductor 

 being split up, or nearly split up, by the Rontgen rays, which 

 act the part played by the solvent in ordinary electrolytic 

 solutions." It has occurred to me that if such ionisation really 



