444 SOME NEW BOOKS [December 



for the purpose of justifying the classification into seven systems ; frequent 

 reference to the optical characters is also made in the detailed description of 

 various crystals. 



Several new terms are employed ; most of the classes formerly known as 

 hemimorphic are called acleistous ; monoclinic crystals are divided into a gonoid, 

 a plinthoid, and a hemimorphic class ; an axis of symmetry which is polar is 

 called uniterminal, a name that appears awkward where all the other terms are 

 of Greek origin. 



The representation of crystal axes by interrupted dots and dashes is of 

 doubtful expediency, since they become difficult to distinguish among other 

 lines ; but the author ingeniously makes use of this contrivance to indicate their 

 " order " when they are axes of symmetry by the numbers of clots. The number 

 of the chapter might have been given at the head of each page, for frequent 

 references are made to previous chapters. 



The reader will perhaps not expect to find a philosophic treatment of the 

 principles which underlie the geometry of crystals in a book designed for the 

 practical instruction of students ; if the subject be new to him he may wonder 

 why a crystal is treated merely as an isolated problem in drawing, projection, 

 and calculation ; but let him master the contents and we think that he will 

 acquire a very considerable knowledge of geometrical crystallography, which 

 will set him thinking about the signification of the beautiful laws which prevail 

 in this subject. 



CLASSES OF CRYSTALS. 



Darstellung der 32 moglichen Krystallklassen. By H. Baumhauer. 

 Leipzig: Engelmann, 1899; 36 pp., 32 figures, and 1 plate. 



Much attention has recently been paid to the subject of crystal symmetry, 

 and the treatment and nomenclature of the 32 classes have undergone many 

 changes. 



In this short pamphlet Professor Baumhauer adds another to several 

 attempts which have been made to describe these classes in a simple and 

 systematic manner. It will be sufficient to say here that he classifies them 

 according to their axes of symmetry, and distinguishes between those which 

 are and those which are not intersections of symmetry planes by the not very 

 happy terms homogeneous and inhomogeneous ; axes perpendicular to a sym- 

 metry plane are distinguished by the equally unsatisfactory term symmetrical. 



The plate which gives a summary of the classes succeeds perhaps better 

 than any previously published, in making the symmetry apparent, and will be 

 of use to teachers. 



EOCK-ANALYSIS. 



Praktische Anleitung zur Analyse der Silicatgesteine. Pp. 8G. Leipzig: 



W. Engelmann, 1899. 



This, as its title further sets forth, is a translation by Dr. E. Zschimmer of 

 the introductory portion of Bulletin No. 148 of the United States Geological 

 Survey, the concluding part of that work being a most valuable series of rock 

 analyses. These analyses are omitted in the translation, which deals only with 

 the analytical methods adopted by Prof. F. W. Clarke and Dr. W. F. Hille- 

 brand in the laboratory of the United States Geological Survey. The methods 

 aim at an exactitude in rock analyses hitherto found wanting in the published 

 work of many of the earlier chemists who have contributed to our knowledge 

 of the composition of rocks. In the analyses given in the Bulletin just cited, 

 extremely small quantities of elements have been detected and estimated in 



