Geology and Mineralogy. 397 



quartz cut normally to the axis S mm thick absorbs 40 per cent. — 

 Trans. Acad, de Lincei ; Nature, July 27, 1893. j. t. 



11. Theory of electrical waves in wires. — A. Elsas in a mathe- 

 matical paper shows that the phenomena observed by Hertz can 

 be explained on the old theories of the movement of electricity, 

 developed by Kirchhoff, " Ueber die Bewegung der Electricitat in 

 Drahten " and also by HelmholtE. Maxwell's theory of electro- 

 magnetic action is therefore not necessary to explain the Hertz 

 effects. Maxwell's theory, however, still remains of value and its 

 truth is not gainsaid by the author. — Ann. der Physik and 

 Chemie, No. 7, 1893, pp. 487-508. J. t. 



12. Polarization of ultra red rays by means of metallic gratings. 

 — H. E. J. G. du Bois and H. Rubers have examined this sub- 

 ject by means of a bolometer which was inserted in the telescope 

 of a suitable spectrometer. The amount of energy transmitted 

 was measured in the two cases when the rays were polarized at 

 right angles and also parallel to the gratings. The authors find 

 a fruitful analogy between the polarization of the heat rays and 

 the polarization of the electrical rays examined by Hertz. 



13. Interference of electrical waves in air. — This has been shown 

 by Klemencic and Czermak in the following manner. A Hertz 

 exciter was placed at th« focus of a parabolic mirror and a resona- 

 tor at the focus of a similar mirror. At the intersection of the 

 axial lines of the mirrors could be slid two parallel plates of glass 

 covered with tin foil. The apparatus, thus, was closely analogous 

 to Fresnel's apparatus for showing by means of reflection from 

 glass mirrors the interference of light waves. The mirrors hav- 

 ing been placed side by side with the exciter at the focus of one 

 and the resonator at the focus of the other, the two plates of 

 glass covered with tin foil were moved parallel to each other 

 along the intersection of the axes of the parabolic mirrors, until 

 the proper difference of path of the waves necessary to produce 

 interference was obtained. To detect resonance — a thermo-element 

 connected with a suitable galvanometer was used. The results 

 showed an interference phenomenon ; but it was of a somewhat 

 confused nature. — Ann. der Physik und Chemie, No. 9, 1893, pp. 

 174-188. J. T. 



II. Geology and Mineralogy. 



1. Iowa Geological Survey, Vol. I. First Annual Report for 

 1892. 8vo, 472 pp., 10 plates and 26 figures. Samuel Calvin 

 State Geologist. Des Moines, 1893. — In addition to brief admin- 

 istrative reports, the first annual report of the Iowa Survey con- 

 tains the following papers : Geological Formations of Iowa, 

 Charles Ilollin Keyes; Annotated Catalogue of Minerals, and 

 Bibliography of Iowa Geology by same author ; Cretaceous De- 

 posits of Woodbury and Plymouth Counties, Samuel Calvin ; 

 Ancient Lava Flows in the Strata of Iowa, Samuel Beyer ; Dis- 

 tribution and Relations of the St. Louis Limestone in Mahaska 



