34Q 



NA TURE 



[February 8, 1906 



OUR BOOK SHELF. 



Die neuere Entwickelung der KristaUographie. By 



Dr. H. Baumhauer. Pp. viii+184; 46 plates. 



(Brunswick : Vieweg and Son, 1905.) Price 4 



marks. 

 Though this sketch of the more recent developments 

 of our knowledge of crystals will be of service to 

 the crystallographic student, it is primarily intended 

 for those physicists and chemists who require to make 

 use of crystallographic methods in their own re- 

 searches ; detailed explanations of technical expressions 

 and crystallographic ideas are therefore given. 



The work is divided into six chapters. The first 

 treats of the definition of a crystal, the law of zones, 

 the law of rationality of indices, and the methods of 

 crystallographic projection ; an account is given of 

 various fluid and viscous bodies which must now, ac- 

 cording to the researches of Lehmann, Schenck, and 

 others, be included in the same group with solid 

 crystals. The second chapter shows that crystals may 

 be distributed into thirty-two classes capable of refer- 

 ence to six systems, each class differing from the others 

 in the elements of its symmetry. The third chapter ex- 

 plains the various methods by which the class of sym- 

 metry to which a crystal belongs may be ascertained, 

 and thus treats of the determination of facial distribu- 

 tion by means of one-circle, two-circle, or three-circle 

 goniometers, and the investigation of the physical or 

 chemical properties, more especially optical anomalies, 

 circular polarisation, pyroelectric behaviour, and the 

 etch-figures developed on crystal faces as a result of sol- 

 vent or chemical action ; the last mentioned is a branch 

 of crystal research to which Dr. Baumhauer has him- 

 self given much attention. The fourth chapter gives 

 a discussion of the regular growths met with in 

 crystals, and in this connection a detailed account is 

 given of mimetic growths such as are observed in 

 the case of the felspars. In the fifth chapter is a 

 description of the development of crystal faces ; an 

 account is given of Goldschmidt's " law of compli- 

 cation " and of nodal points. The sixth and last 

 chapter deals with isomorphism, morphotropy, topical 

 axes, polymorphs, and the relations between the chemi- 

 cal formula and the crystal system of a substance. 

 The observations of Prof. Miers relative to the vicinal 

 faces of alum crystals, and the researches of Dr. Tutton 

 on the relation between the chemical composition and 

 the morphological and physical properties of a sub- 

 stance are specially mentioned. Prof. Baumhauer's 

 long experience as a teacher has enabled him to give 

 an account which is at once well up to date and of a 

 readable character. 



La Theorie moderne des Phinomenes physiques. 



Radio-activitd, Ions, Electrons. By Prof. Augusto 



Righi. Pp. iv+125. (Paris: L'Eclairage Elec- 



trique, 1906.) 

 This is a translation from the Italian. The book is 

 a good semi-popular account of recent physical de- 

 velopments, and is likely to be useful to those desirous 

 of gaining a first acquaintance with them. Even 

 original investigators will here and there glean useful 

 hints or ideas. 



Prof. Righi, we are interested to note, prefers the 

 use of an electroscope of almost microscopic dimen- 

 sions for detecting minute radio-active effects. A 

 systematic inquiry into the best dimensions for these 

 instruments is very desirable, and might be advan- 

 tageously made either from a mathematical or from 

 an experimental standpoint. 



In one or two cases Prof. Righi quotes investi- 

 gations of which the soundness may perhaps be 

 doubted — for instance, the alleged occurrence of 

 radiations from phosphorescent zinc sulphide capable 



no. 1893, vol. 73] 



of penetrating opaque bodies, and the determination 

 ol the velocity of Rontgen rays made by M. Blondlot. 

 This last experiment depended on the action of the 

 Rontgen tube on a minute electric spark. This 

 action was afterwards attributed by M. Blondlot to 

 the H-rays, and the objective existence of the >i-rays 

 is now generally discredited. 



We have seen an English translation of Prof. 

 Righi 's book. The French translation is not, there- 

 fore, of special interest to English readers. 



R. J. S. 



Modem Lightning Conductors. By Killingworth 

 Hedges. Pp. viii+119. (London: Crosby Lock- 

 wood and Son, 1905.) Price 6s. 6d. net. 

 The subject of lightning protection is one of consider- 

 able importance to architects, and a book in which the 

 existing information thereon is conveniently collated 

 is therefore to be welcomed. Mr. Killingworth 

 Hedges 's long association with this very special branch 

 of electrical engineering enables him to write with 

 authority. The book may be regarded as a very 

 useful work of reference on the subject, as it contains 

 a summary of the recommendations of the lightning 

 research committee of 1905, together with numerous 

 extracts from the observers' reports on buildings which 

 had been struck by lightning, which served as the 

 basis on which the committee drew up its sugges- 

 tions. These extracts are copiously illustrated and 

 the faults in the details of the protection in each case 

 are clearly pointed out. The book is enlivened by the 

 last chapter, which gives several instances of peculiar 

 results of lightning strokes. 



LETTERS TO THE EDITOR. 



[The 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 tliis or any other part of Nature. 

 No notice is taken of anonymous communications.] 



The Inventor of the Nicol Prism. 



Can any of your readers supply me with the dates of 

 birth and death of William Nicol, the inventor of the 

 Nicol prism? There is a tablet to his memory in the 

 Wariston Cemetery, in Edinburgh, bearing an inscription 

 drawn up by the late Prof. Tait. Strange as it may seem, 

 though his fame is world-wide in optics, he is not even 

 mentioned in the " Dictionary of National Biography," 

 nor do I know of any memoir of him elsewhere. 



Silvanus P. Thompson. 



Technical College, Finsbury, London, E.C., February 6. 



Result of War affected by Soldier's Stature. 



The Japanese had an unquestionable advantage in the 

 recent war as being smaller than the Russians ; they were 

 smaller targets for fire-arms. I wish to point out that 

 it is possible to express this advantage quantitatively on 

 the assumption, justifiable in modern war, that bullets 

 are, on the average, uniformly distributed over the target 

 presented by a man's body, also that a man presents a 

 target proportional in area to the square of his height. 

 The Anthropological Institute has kindly given me figures 

 for the purpose ; the average height of 2500 Japanese, 

 1260 of them being soldiers, was 1585 millimetres as com- 

 pared with an average of 1642 millimetres for the average 

 of 177,948 European Russian conscripts. The average 

 Russian height thus exceeds that of the Japanese by about 

 3-47 per cent. The squares of the two average heights, 

 representing, as I have said, the average targets offered 

 by each to an enemy, differ therefore approximately by 

 7 per cent., so that the Russian fire was relatively in- 

 effective to that extent. John H. Twice. 



The Hydro, Ben Rhydding, Yorkshire, February 1. 



