Notices respecting New Books. 145 



between 550 and 740, and the accounts of them, varying in length 

 from 17 pages downwards, have for the most part been revised by 

 the respective authors. While serving as a guide' to the original 

 papers, the " Annals " is primarily intended for those who cannot 

 see the originals at all, and is therefore planned so as to contain 

 in itself in the course of a few years the whole body of recent 

 Geological knowledge in this country. 



We are glad to find that there is an increasing public support 

 of this useful work ; and that, if the present volume proves to be 

 self-supporting, we may look hopefully to its future. 



The Morphology of Crystals. By Professor N. Story Maskelyne, 

 F.R.S. (Clarendon Press. 1895.) 



The appearance of Prof. Maskelyne's long-expected book is an 

 event of considerable importance in the mineralogical world. The 

 lines on which the book is written were fixed some twenty years or 

 more ago, and a good deal of it has been long in print. One cannot 

 help regretting that Prof. Maskelyne had not the courage to publish 

 the book in parts. The first 150 pages or more are, we fancy, much 

 in the same state that they were twenty years ago. They contain 

 the general propositions which hold for all crystals, and amongst 

 others the elegant proof of the theorem, that the only angles 

 possible between planes of symmetry in a crystal are one or other 

 of the four following— 60°, 90°, ±20°, and 180°. This proof 

 Prof. Maskelyne used to give more than twenty-five years ago 

 in his lectures at Oxford, but it has remained inaccessible to the 

 generality of students. 



Prof. Maskelyne may, in his manner of regarding the subject, 

 be almost classed as a member of the Vienna school of Grailich 

 and von Lang. He adopts, as they did, planes of symmetry as the 

 all important elements in classification, and axes of symmetry 

 receive but a small amount of attention. In the last decade there 

 has been a very decided movement in the direction of regarding 

 crystal forms as resulting from the general principles of symmetry, 

 and more especially to base the subdivision into types on the 

 nature and number of the axes of symmetry. This latter method 

 is certainly more logical, and has rendered it needless to talk of 

 planes, or axes, of symmetry being in abeyance. A crystal has 

 certain elements of symmetry which have, if many coexist, definite 

 relations existing between them, and which in themselves form a 

 complete cycle. The application of the methods of analytical 

 geometry to the representation of crystal faces may, however, owing 

 to the law of rational indices, indicate the possibility of faces which 

 have a higher geometric symmetry than that of the crystal. AVe 

 may illustrate this by a truncated cone of cannon-balls. If the balls 

 be spheres, the base and planes of truncation will clearly be exactly 

 similar parallel faces. If the shot be modern cylindrical ones 

 pointed at one end, and if these be placed in the pile with the base 

 downwards, the base and plane of truncation will be parallel but 



Phil. Mag. S. 5. Vol. 40. No. 242. July 1895. L 



