Geology and Mineralogy. 433 



8. Reflection of Cathode rays. — H. Starke proves by a method 

 which he believes to be superior to those hitherto adopted, that 

 cathode rays are reflected in different degrees by different metals. 

 At perpendicular incidence, platinum reflects 36 per cent. This 

 proportion does not change appreciably with changes of charging 

 potential from 6000 volts to 9000 volts. — Wied. Ann., No. 9, 

 pp. 49-60, 1898. j. t. 



9. Change of the energy of Cathode rays into light rays. — 

 E. Wiedemann measures the proportion of energy of the cathode 

 rays which is converted into light rays and finds that the propor- 

 tion converted into light is of the same order as that in the case 

 of photoluminescence and is very small. — Wied. Ann., No. 9, pp. 

 61-64, 1898. j. t. 



10. The Theory of the Coherer. — Since the discovery of Branly 

 that electrical waves can diminish the resistance of tubes filled 

 with fine metallic particles, many investigators have endeavored 

 to ascertain the cause of the phenomenon. The recent experi- 

 ments in wireless telegraphy have given great interest to this 

 inquiry. D. van Gulik reviews the various theories proposed, 

 and in view of his own experiments inclines to the belief that the 

 action is due to minute' sparks between the particles, which break 

 down the separating oxide or intervening medium, and the torn 

 off particles resulting from the disruptive sparks build a conduct- 

 ing bridge. He objects to the new term "Frittrohren " intro- 

 duced by Slaby.— Wied. Ann., No. 9, pp. 136-145, 1898. 



E. Dorx has carried out a very complete series of experiments 

 to test the theories of the coherer. The degree of moisture of the 

 pulverized substances greatly affected the results. Oxides of 

 iron, of zinc and of copper appeared to possess the greatest con- 

 ductibility ; aluminum and its oxides the least. — Wied. Ann., 

 No. 9, pp. 146-161, 1898. j. t. 



11. Absorptio?i of light produced by a body placed in a magnetic 

 ■field. — Auguste Rigiii discusses phenomena of absorption due to 

 the Zeemann effect. A beam of light from the sun or an electric 

 light is polarized by a nicol prism and sent through the axis of 

 a powerful Ruhmkorf magnet. This beam is extinguished by a 

 second nicol. Between the poles of the magnet is placed a 

 sodium flame. The yellow light is not extinguished on turning 

 the analyzer ; on the contrary it becomes white and more and 

 more intense. The author discusses the theory of the experiment 

 from the point of view of Zeemann. — Comptes Rendus, July 25, 

 1898, p. 217. j. t. 



II. Geology and Minekalogy. 



1. 18th Annual Report of the Director of the U. S. Geologi- 

 cal Survey, 1896-97 (Extract from 18th Ann. Rept., Pt. I), C. D. 

 Walcott, Director; pp. 1-130, two folded maps. Washington, 

 1897. — During the year covered by this Report the sum of 

 $568,690 was appropriated for the work of the United States 



