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 dots. 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 ina 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. 
ROCK-ANALYSIS. 
Praktische Anleitung zur Analyse der Silicatgesteine. Pp. 86. 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 
