512 Scientific Intelligence. 



The second part of the work is devoted to a description of the 

 rock-making minerals. In this the matter is considerably con- 

 densed to bring it within the limits of the work. The essential 

 material only is given and the subject matter of the less common, 

 or less important species, is more condensed by use of smaller 

 type. A set of tables, such as are found in most of the well- 

 known texts, concludes the work. 



The translator has done his part of the work carefully and well. 

 The book is well printed and attractively bound, and is illustrated 

 by numerous diagrams, cuts, and half tones, which add greatly 

 to the understanding of the text. While the work will not 

 replace the more comprehensive manuals, which are necessary to 

 the advanced students and teachers of petrography, it will, with- 

 out doubt, find a very useful field of its own with beginners and 

 with those who desire a simpler method of treatment of the sub- 

 ject matter. l. v. p. 



9. The Methods of Petrographic-Microscopic Research; by 

 Fred. Eugene Wright. 8°, pp. 204, 11 plates, 118 figures, 1912. 

 Carnegie Institution, Washington. — This work is almost the 

 antithesis of the one noticed above. Its intent is seen in the sub- 

 title, which reads " Their relative accuracy and range of applica- 

 tion." It is probably the most serious, scholarly and generally 

 comprehensive investigation of the optical methods employed in 

 petrographic research, to the extent indicated in the sub-title, 

 which has yet appeared, and it cannot fail to have a great 

 influence in promoting more careful and thorough work along 

 these lines. It is in no sense a text-book, and is no work for 

 beginners, but it is one which should be in the hands of every 

 teacher and advanced worker in petrography. It begins with an 

 investigation of the microscope, which is thoroughly discussed as 

 an instrument of precision in optical research. After this various 

 subjects, such as color, pleochroism, optical characters of bire- 

 fracting substances, refractive indices, birefringence and its meas- 

 urement, extinction angles, optic axial angles, etc., are treated in 

 successive chapters. The various methods and apparatus invented 

 in recent years, largely by the author, in the Geophysical Labor- 

 atory of the Carnegie Institution, are for the most part usefully 

 included. A series of carefully constructed plates, using various 

 modes of projection, furnish, by graphic methods, quick and easy 

 solutions of problems of determination, as, for instance, to reduce 

 the optic angle observed in air to be the true angle in the sub- 

 stance, when the index of refraction is known. 



It is work of this character, the result of careful, accurate, 

 intelligent and highly trained effort directed to a particular field 

 of science, that makes the productions of the institution which 

 produces them of such a high degree of merit. l. v. p. 



10. The Soil Solution : The nutrient medium for plant growth; 

 by Frank K. Cameron. Pp. iv, 125, with Index and 3 ills. 

 Easton, Pa., 1911 (The Chemical Publishing Co.). — For some 

 years the Soil Survey at Washington has been engaged, among 



