2-]2 



NATURE 



[May 



o« 



1910 



angles were measured, and upwards of four hundred 

 sections, and the same number of prisms, have been 

 cut. The optical study incidentally raised some inter- 

 esting points in connection with the phenomenon 

 known as crossed-axial-plane dispersion. Beautiful 

 photographs of the interference figures given by 

 caesium magnesium sulphate in light of different 

 wave-lengths at ordinary temperatures and at 78° 

 are reproduced on p. 169. The thermal expansion of 

 the sulphates of potassium, rubidium, and caesium 

 alone have as yet been determined ; the exacting nature 

 . of this work may be gathered from the remark on 

 p. 71 that each series of observations, sixty-four in 

 all, entailed five hours' continuous labour. 



Certain definite conclusions have been established 

 by Pr. Tutton's work. The variation in the morpho- 

 logical and physical properties of the members of the 

 same isomorphous series, though slight, is progres- 

 sively related to the atomic weights in the case of 

 the three elements belonging to the same family 

 group. The relations between members containing 

 these elements are, indeed, so intimate that they may 

 be regarded as forming an inner circle — a eutropic 

 series, as it is termed — within the isomorphous series ; 

 members containing ammonium and thallium, though 

 •undoubtedly belonging to the same isomorphous 

 -series, show greater deviations from the general pro- 

 perties. Corresponding changes of the same order, 

 "but in the reverse direction, take place when selenium 

 is substituted for sulphur. The results are so tabu- 

 lated that the relations and differences are easily 

 .grasped. 



Throughout the book Dr. Tutton has realised the 

 importance of not intruding upon observed facts 

 about which no possible doubt could be raised any 

 .speculative matter which might be open to dispute, 

 and he refrains from dwelling at any great length 

 -upon the many interesting questions relative to 

 molecular arrangement which are suggested by the 

 results of his investigations. He does, however, 

 argue that the possibility of ammonium replacing a 

 •single atom without much effect upon the crystalline 

 form is incompatible with Barlow's theory of close- 

 packing, which has recently been attracting so much 

 atterltion. On the other hand, Pope and Barlow, in 

 their first paper, discussed the isomorphism of potass- 

 ium chloride and ammonium chloride, and showed 

 that the relationship in this case was in strict conso- 

 nance with the close-packing of the spheres of influ- 

 ence. Close-packing is, indeed, merely a way of 

 representing the state of equilibrium between the 

 mutual interactions of atomic forces emanating from 

 definite centres ; it is difficult to attach any physical 

 significance to loose-packing in connection with crys- 

 talline structure. 



Enough has been written to show that the book 

 is one that should be read and studied by all inter- 

 ested in crystals, their properties, and their formation. 

 Finally, we hope that Dr. Tutton may enjoy, for 

 many years to come, health and strength to carry 

 on the splendid work that constitutes his recrea- 

 tion. 



NO. 2 1 14, VOL. 83] 



SOIL MANAGEMENT AND PLANT GROWTH. 



The Principles of Soil Management. By Profs. T. 

 Lyttleton Lyon and E. O. Fippin. Pp. xxxiii + 53i. 

 (New York: The Macmillan Company; London: 

 Macmillan and Co., Ltd., 1909.) Price 75. 6d. net. 



THIS book is the first of a new series designed by 

 Dr. Bailey for " class-room work and for special 

 use in consultation and reference," and the volumes] 

 are therefore larger and fuller than those of the Rural 

 Science Series, which were meant for general readin) 

 and popular use. In the present series the subject is 

 to be presented in such a way that it shall develof 

 '•clear thinking, sound argument, constructive 

 imagination, and effective application to the needs of 

 life." 



Dr. Bailey contributes a vigorous introduction, 

 strong in its condemnation of.nour present lack of 

 interest in soil problems. 



"We are accustomed," he says, "to think of the 

 power of man in gaining dominion over the forces of 

 nature,— he bends to his use the expansive powers of 

 steam, the energv of electric currents, .... but while 

 he is doing all this he sets at naught the powers in the 

 soil beneath his feet, wastes them, and deprives him- 

 self of vast sources of energy." 



Among the national resources that demand conser- 

 vation the soil takes a high rank. 



Turning to the volume itself, the subject is treated 

 under seven headings; the soil is considered as a 

 medium for root development; as a reservoir for 

 water ; as a source of plant food ; the organisms of the 

 soil are studied, the composition of the soil air, and 

 the relation of soil to temperature. Finally, methods 

 of soil management are discussed. The general idea 

 is to treat the soil as a medium for plant growth, 

 to regard it from the agricultural and not so much 

 from the geological point of view. There is, of 

 course, no partfcular novelty in this position, and 

 several books have already been written in which the 

 subject is dealt with in the same way ; the arrange- 

 ment of the matter therefore calls for no comment. 



Liberal use is made of photographs to illustrate 

 the various poi"ts brought up, and there are some 

 very good photomicrographs showing the structure 

 of certain common rocks. A considerable amount of 

 time and trouble must have been spent on these, and 

 also on the tables of figures which have been pretty 

 freelv introduced. The results obtained at the various 

 experiment stations in the United States have been 

 drawn on, and a good deal of material is collected 

 that will be new to the English reader and mterestmg 

 to the American student. 



But when all this is said, it must be admitted that 

 the book somehow leaves an unsatisfactory impreci- 

 sion. In spite of the attractiveness of the subject, 

 the present writer has to confess that he found the 

 volume rather boring. It is hardly a book that the 

 American student would "enthuse" about, and it 

 does not adequately repay all the labour that must 

 have been bestowed upon it. We somehow get a 

 suspicion that the authors have searched more 

 amongst the latest text-books and the latest bulletins 



