NA TURE 



439 



THURSDAY, FEBRUARY i, 1912. 



THE STUDY OF CRYSTALS. 



1) Crystallography and Practical Crystal Measure- 

 ment. By Dr. A. E. H. Tutton, F.R.S. Pp. xiv+ 

 946, with 3 plates and 720 figures in the text. 

 I (London : Macmillan and Co., Ltd., 191 1.) Price 

 305. net. 



t) Crystals. By Dr. A. E. H. Tutton, F.R.S. 



Pp. X + 301, with 24 plates and 120 fig'ures in the 



text. (London : Kegan Paul, Trench, Triibner and 



Co., Ltd., 191 1.) Price 55. (The International 



Scientific Series.) 



'HE rapid advances which have been made in 



recent years in our knowledge of crystals, and 



le increasing number of points at which crystallo- 



raphy comes into contact both with chemistry and 



lysics, render it more than ever desirable that 



Students of these sciences should acquire a sound 



Cnowledg'e of the nature and properties of crystals 



Ind an acquaintance with the methods of crystallo- 



raphic research. In illustration of this it is only 



iiecessary to refer on one hand to the work of Pope 



id Barlow on the relation between valency and 



i^stalline structure, and on the other to that of 



..ehmann, Vorlander, and others on the remarkable 



roup of bodies forming the so-called "liquid 



.'stals." 



Although numerous excellent treatises on crystallo- 

 graphy have been published in recent years in Ger- 

 lany and France, in England the number of works 

 levbted to this subject has been very limited, and, 

 intil the recent appearance in America of a transla- 

 ^n of the optical section of Prof. Groth's well-known 

 jok, the only information available on the physical 

 ide in English has been that contained in the intro- 

 ictory portions of text-books of mineralogy. There 

 iras thus ample room for a new book, and Dr. 

 Tutton 's volume on "Crystallography and Practical 

 Crystal Measurement " (i) will be welcomed by all 

 rorkers in the subject. Although in some respects 

 ^complete, its v('r\ full treatment of what are, from 

 ie practical poini of view, the most important 

 ranches, viz. crys!;il iik asurement and optics, render 

 a valuable and impurfant addition to the literature. 

 The book is essentially a practical one, and is 

 iehiefly concerned with the methods of determining 

 fte form of crystals and of measuring their various 

 lysical constants; but attention is also given to the 

 iderlying matters of theory. It is divided into two 

 |>arts of nearly equal length, dealing rcspectivelv 

 rith the morphology and the physical properties of 

 crystals. 



The practical and theoretical portions of the sub- 

 ject are treated side by side, in successive chapters. 

 ' 'nis, in part i., after a short introduction on the 

 '' are of crystals, a description of the method of pre- 



I iiing suitable crystals for measurement is followed by 

 .1 chapter on the goniometer, and this is at once illus- 



II ited by an account of the actual measurement of a 

 I I \ stal of potassium sulphate. The succeeding 

 • liapters treat of axes and fhc law of rationality, 



NO. 2205, VOL. 88] 



zones and the stereographic projection, and the 

 formulae required in calculation ; and the measurements 

 of the crystal previously made are then worked out in 

 detail. An account is next given of the theories of 

 crystals as homogeneous structures, and of crystal 

 symmetry and its thirty-two types. Chapters xi. to 

 xxiv. are devoted to an account of the crystal systems 

 and the various forms possible in each of the thirty- 

 two classes, the discussion of each system being fol- 

 lowed by a full account of the measurement and 

 calculation of one or two crystals belonging to it. 



Among" subjects dealt with in later chapi. r^ may 

 be mentioned goniometry at higher temperatures and 

 the change in the angles of crystals on heating, gonio- 

 meters with two and three circles and the gnomonic 

 projection, the density, volume, and structure of 

 crystals and the calculation of their molecular "dis- 

 tance ratios." Part i. ends with a useful account of 

 Fedorov's theory of cubic and hypohexagonal types, 

 and a short reference to the theory of Pope and 

 Barlow on valency-volumes. 



The description of Fedorov's theory and his method 

 of arriving at the correct mode of setting up a 

 crystal in accordance W'ith its structure, is especially 

 noteworthy as containing the first account which has 

 appeared in English of his method of " crystallo- 

 chemical analvsis," by means of which it will be 

 possible to identify, after measurement of its crystals 

 and reference to an index, any chemical substance 

 of which the crystalline data have been iiu-(ir|)orated 

 in the index. The method is not yet available for 

 general use, but in the hands of Prof. Fedorov it has 

 already proved very successful under numerous tests, 

 and seems likely in the future to prove of great 

 service to the chemist. 



In the chapters on crystal axes, zones, and indices, 

 as well as in those on crystalline symmetry, the stereo- 

 graphic projection, &c., proofs have perhaps wisely 

 been omitted; but some explanation of the meaning 

 of the numbers forming a zone-symbol might well 

 have been included. 



The second, or physical part of the book (pp. 547- 

 933) is devoted almost entirely to the discussion ot the 

 optical properties of crystals and the miMhods ot (l.t<T- 

 mining them. The methods of measuriiii; tli. . \pan- 

 sion of crystals by heat and their elastic properties 

 bv means o! the author's interference-apparafus. are 

 also described, and the last chapter contains a short 

 account of the hardness of crystals, and of liquid 

 crystals, and the use of the "crystallisation micro- 

 scope." No reference is made, however, to other 

 physical properties, such as pyro-, piezo- and thermo- 

 electricity, and thermal and electric conductivity. 



The first eight chapters in this part (pp. 545-<>*^') 

 are occupied with a discussion of the nature of light 

 and the mode of its transmission through crystalline 

 media, while the rest of the optical portion (pp. (>Si- 

 883) is chiefly devoted to a description of the instru- 

 ments and operations required for th- m. a-m.-nicnt 

 of tlie various properties exprcssibl" '>> ' ■ Imm and 

 orienlation of the optical ellipsoid • iMiriinn in- 



cludes detailed directions for the cutnng and fjrindinj; 

 of prisms and plates, the production of monochromatic 

 light of any desired wave-length, the determination 



