546 Scientific Intelligence. 



Errors. Ohmic Resistance," III " Null Methods. Resistance 

 Measured by Differential Instruments," V " Wheatstone-b ridge 

 Methods. Variable Rheostat. Arrangements of Resistances. Per 

 Cent Bridge. Suggestions for Using Bridge," YII " The Deter- 

 mination of Electrical Conductivity," IX "Insulation Resistance 

 of Cables," X " Resistance as Determined with Alternating Cur- 

 rent," XI " Resistance Measurements when the Resistance In- 

 cludes an Electromotive Force," XII " Elementary Principles of 

 Fault Location," XIII "Measurement of Temperature by the 

 Measurement of Resistance," and XV " Deflection Instruments 

 and Galvanometers." The appendix contains much useful mate- 

 rial. Finally, a novel feature of the composition of the book con- 

 sists in numbering the articles of each chapter with the same 

 multiple of 100 as is the number of the respective chapter. Thus, 

 the articles of Chapter XII are numbered consecutively from 1200 

 to 1217 inclusive. In like manner the figures have the same num- 

 bers as the articles to which they pertain. h. s. u. 



14. Stabilitdt, Labilitdt und Pendelungen in der Elektrotechnik y 

 by Hans Busch. Pp. viii, 246, with 69 figures. Leipzig, 1913 

 (S. Hirzel). — This monograph is a revised and much amplified pre- 

 sentation of the author's doctoral dissertation at the University 

 of Gottingen. As the title partly suggests, the book is chiefly 

 devoted to a discussion of the conditions and criteria for stability, 

 instability, and forced vibrations in dynamos and electric motors 

 of various types. The first three chapters are mainly theoretical 

 while the fourth and last chapter deals with the practical applica- 

 tions of the preceding. h. s. u. 



II. Geology and Mineralogy. 



1. The formation of Coal beds ; bv John J. Stevenson. 

 Pt. Ill, Proc. Amer. Phil. Soc, vol. li/ pp. 423-553, 1912.— In 

 this readable work Professor Stevenson discusses the nature of 

 the rocks of the Coal Measures and their mode of deposition in 

 the northern Appalachian basin. The general stratigraphy and 

 areal distribution of the formations and the irregular deposition 

 of the sediments are treated in the opening part of the work. 

 Then follows a discussion as to the significance of rounded frag- 

 ments of coal in sandstone, how the sandstones and shales includ- 

 ing the red beds were deposited, the nature of the marine and 

 freshwater limestones and the testimony of the fossils as to depth 

 of water. There is a wealth of information here for students of 

 sedimentation and for stratigraphers, to all of whom the paper is 

 commended. 



The article tells of the work of mighty rivers, whose valleys were 

 periodically invaded by shallow and narrow seaways, with waters 

 more or less prolific in marine animals. The following are some 

 of the author's conclusions : 



