Geology and Mineralogy. 155 



line passing through its middle, caused by the shadow of the 

 string when it crosses the slit. When the string vibrates this 

 shadow draws, so to speak, the vibration of the string on the sen- 

 sitive paper. A large number of results accompany the paper. 

 The effect of bowing the string near the nodes, is discussed. — Ann. 

 der Physik unci Chemie, No. 12, 1891, pp. 623-641. j. t. 



12. The Telephone as an optical instrument for current meas- 

 ure. — M. WiEisr affixes a stylus to the diaphragm of a telephone. 

 This stylus touches a mirror which is fastened to a flexible arm, 

 which in turn is clamped in an adjustable support. The mirror 

 holder is tuned carefully to the note of the diaphragm and the 

 latter is also tuned to the note of the alternating current which 

 is employed. The instrument readily shows 3 , 10"' J amperes. — 

 Ann. der Physik and Chemie, No. 12, 1891. pp. 681-688. J. T. 



13. Solubility of Glass. — F. Kohlrattsch has completed an 

 •exhaustive paper on this subject. Among the large number of 

 results obtained by him, it is noted that glass containing silicic 

 acid, boracic acid, alkali without chalk, show little solubility. 

 Borax glass without silicic acid is enormously soluble. — Ann. 

 d,er Physik und Chemie, No. 12, 1891, pp. 577-622. j. t. 



14. An Introduction to the Mathematical Theory of Electricity 

 and Magnetism ; by W. T. A. Emtage. 228 pp., Oxford, 1891. 

 — This little volume gives an excellent introduction on the mathe- 

 matical side to the subjects of Electricity and Magnetism, and 

 will be very useful to the student who does not wish to plunge at 

 once into one of the larger treatises. The method of presentation 

 and the statement of definitions are very clear and systematic. 



II. Geology and Mineralogy. 



1. Tenth Annual Report of the IT. S. Geological Survey, 

 1888-89. — J. W. Powell, Director. In this Report, the report 

 of the Director and the Administrative reports of the Heads of 

 Divisions, occupying 252 pages, are followed by three memoirs 

 of great value, entitled : General account of the freshwater 

 morasses of the United States, with a description of the Dismal 

 Swamp district of Virginia and North Carolina, by Prof. N. S. 

 Shaler, with plates VI to XIX ; The Penokee Iron-bearing series 

 of Michigan and Wisconsin, by R. D. Irving and C. R. Van 

 Hise, with plates XX to XL VII ; and The Fauna of the Lower 

 Cambrian or Olenellus Zone, by C. D. Walcott, with plates 

 XLVII to XCVIII. — A second volume of 123 pages constituting 

 Part II. of the Report, is devoted to the subject of the Irriga- 

 tion Survey. 



Professor Shaler treats of the formation of morasses, and the 

 •conditions favorable to it in climate, vegetation and position, and 

 enters into the history, geological structure and economic value 

 •of the region of the Dismal Swamp, illustrating the subject with 

 many sections and fine plates. The paper by Professors Irving 

 and Van Hise describes with fulness the rocks and structure of 



