546 



NATURE 



[June 22, 191 1 



tin! parallelism, same-ways orientation, of the struc- 

 tural units, and to develop systematically in stages, 

 starting from parallelism in the holohedral class of a 

 crystal system, the possibilities of alternation 

 and other forms of partial parallelism. The 

 idea is justified from two points of view, 

 first, that of the simplification for the student, 

 who can readily construct the fourteen models of the 

 Bravais space-lattices, by means of knitting needles 

 and spherical balls impaled on them, and indicate on 

 them if he chooses the stages of parallelism, corre- 

 sponding to the various classes, by means of little 

 inclined rods or other devices for indicating differences 

 in the nature of the nodes of the space-lattice; and 

 secondly, from the point of view of the undoubted 

 importance of the space-lattice as regards crystal 

 structure, and the fact that the space-lattice represents 

 the arrangement of the molecules, while the Sohnckian 

 points clustered around its nodes represent the ar- 

 rangement of the atoms, and that models of such 

 Sohnckian systems of points ar^ very difficult to 

 construct. 



An excellent series of stereoscopic photographs of 

 the fourteen space-lattices are given, forming quite a 

 feature of the book, the photographs not merely re- 

 presenting the spherical balls on the steel rods but 

 the shape in stereographic projection of the solid 

 formed by the elementary cell or unit "brick" of the 

 crystal edifice. The photographs were taken from 

 models in the laboratory of Prof, von Groth at 

 Munich. It is interesting to note also that the system 

 of closest packing, as used by Pope and Barlow, is 

 adopted in the book. 



After a few pages of instruction in the elementary 

 facts and nomenclature of crystallography, the author 

 passes on to compare holohedral and partial sym- 

 metry, and shows how by placing a short inclined 

 stroke, rod, or bar at each point of intersection or 

 node of a space-lattice, and doing so either parallel- 

 wise or in an alternately arranged manner, the idea 

 of parallelism or otherwise, and even of a screw- 

 arrangement, may be indicated directly on the space- 

 lattice itself, the disposition of the cluster of 

 Sohnckian points about each node of the space-lattice 

 being thus indicated by the mode of arranging the 

 little stroke or rod. It is shown that such an ar- 

 rangement fulfils Wiener's principle, that homo- 

 geneity consists in the continual repetition through- 

 out space of the same relation between an elementary 

 atom and the entire structure. The diagrams in the 

 second part of the book indicate how this idea of con- 

 structing all the variations of class symmetry of a 

 crystal-system on separate models of the same space- 

 lattice can be carried out, and the book is well worth 

 attention on account of the simplification which it 

 thus presents of the admittedly most difficult part of 

 crystallography. The difference between right- and 

 left-handed mirror-image forms is also very clearly 

 brought out. 



While the particular mode of applying these ideas 

 of Prof. Sommerfeldt is new, it can scarcely be said 

 that the principle is. For Mr. Barlow long ago 

 employed models of the human hand at the nodes 

 of the space-lattice, or about them, to indicate orienta- 

 NO. 2173, VOL. 86j 



tional differences of the atomic cluster which each 

 such node represents. But the present mode of 

 differentiation employed by the professor of mineralogy 

 of Tubingen has the especial merit of emphasising 

 in an unmistakable manner the importance of the 

 space-lattice as the fundamental basis of crystal 

 structure. A. E. H. T. 



MODERN EXPLOSIVES. 



Lcs Explosifs nwdernes. By Paul F. Chalon. 

 Troisi^me Edition. Pp. 787. (Paris : Librairie Ch. 

 B^ranger, 191 1.) Price 25 francs. 



THIS volume is really an encyclopaedia on the sub- 

 ject of explosives, although many of the mate- 

 rials described, however interesting, are scarcely to 

 be regarded as explosives, for U. is only in very excep- 

 tional circumstances that they can behave as such or 

 enter into the composition of explosive mixtures. 



The book is divided into five parts, dealing respec- 

 tively with (i.) explosive substances and the primary 

 materials employed in the industry ; (ii.) the manufac- 

 ture of powders and explosives ; (iii.) pyrotechny ; (iv.) 

 the methods of employing powders and explosives; 

 (v.) employment of explosives for mining and various 

 other applications ; (vi.) legislation. 



It would indeed be difficult to turn to the book for 

 information on any substance which has either been 

 employed or suggested for use as an explosive for any 

 purpose, and the author has certainly carried out the 

 descriptive part of the work in a thorough manner, 

 the recent improvements in manufacture, for example, 

 with guncotton and nitroglycerine at Waltham Abbey, 

 being satisfactorily dealt with. 



No doubt the author as a mining engineer feels 

 the necessity of including much matter which is fami- 

 liar to the chemist or manufacturer, such, for example, 

 as the percentage composition of common salts, the 

 different series of hydrocarbons, alcohols, &c., 

 but it is to be regretted that chemical for- 

 mulae are so frequently incorrectly given that a 

 lengthy errata, mainly to correct these chemical faults, 

 is required, but even this fails to cover all the sins 

 of commission. 



Many interesting substances, unfamiliar even to 

 those engaged in the industry, are briefly described, 

 such as the remarkable crystalline explosive salts re- 

 sulting from the electrolysis of solutions of antimony 

 with an antimony anode, the sulphides and selenides 

 of nitrogen, the sulphide of carbon CgS^, which com- 

 pares with iodide of nitrogen in sensitiveness. In 

 dealing with the explosive nature of compressed 

 acetylene, the author states that its use has had to 

 be abandoned in view of its explosive character, yet 

 by the simple compression into steel cylinders con- 

 taining porous blocks saturated with acetone, acetylene 

 is now a valuable commercial product, and is largely 

 employed in conjunction with oxygen for cutting steel 

 plates, welding, and other purposes where a high 

 temperature is demanded. 



The author's connection with mining ensures that 

 the application of various explosives for blasting pur- 

 poses, submarine blasting for the removal of ob- 

 structions to navigation, including sunken vessels, is 



