Geology and Natural History. 159 



the other it showed no signs of destruction. — Nature, p. 177, Dec. 

 22, 1892. J. x. 



8. Interference of Electric Waves. — A Ruhmkorf coil was made 

 to vibrate 130 times per second by means of a thermopile. To 

 one of its terminals was attached a copper wire ending in a hook, 

 to which a linen thread soaked in calcium chloride was attached 

 by one end, the other hanging free. One of the terminals of a 

 telephone was placed in contact with the thread, the other being 

 isolated. The sound in a telephone was completely extinguished 

 at a certain distance from the copper. When both ends of the 

 thread (which was 3 m long), were connected by fine copper wires, 

 two points of extinction were reached, one from each end. On 

 shortening the thread these points approached each other and 

 formed a zone of extinction between them. This zone of extinc- 

 tion spread over the entire copper wire as the thread was short- 

 ened to zero. The neutral zone is due to interference of two 

 waves of the same period and of equal potential meeting in 

 opposite directions. — Comptes Hendus, Nov. 14, 1892, Nature, 

 Nov. 24, 1892. j. t. 



9. Explanation of HalVs phenomenon. — E. Lommel in a pre- 

 liminary notice, states that by means of a suitably strong current, 

 magnetic filings sprinkled upon a conducting plate will arrange 

 themselves so as to form a beautiful representation of the equi- 

 potential lines of the current. When this conducting plate is 

 brought into a magnetic field these magnetic force lines alter in 

 length and the stream lines of the current, perpendicular to the 

 magnetic force lines, also change, and in these changes can be 

 found an explanation of the Hall phenomenon. — Ann. der Physik, 

 No. 12, 1892, p. 766. j. t. 



10. A Mercury Voltaic arc. — H. Avon has succeeded in pro- 

 ducing a mercury vapor light, of great intensity, by suitably 

 inclining a column of mercury held in a 12 shaped tube which is 

 connected at its point of greatest curvature with a straight tube 

 which is provided with a T-shaped connection, which allows con- 

 nections to a manometer and to an air pump. When the column 

 of mercury in the inverted U-tube is caused to separate at its 

 bending by a slight shock a Voltaic arc results at this point 

 which fills the whole section of the tube with an extraordinarily 

 intense light. Avon gives a list of the spectrum lines which he 

 has measured by means of this light. In addition to the thirteen 

 lines measured by Kayser and Runge, he finds twenty more. — 

 Proceedings of the Physical Society of Berlin, Oct. 21, 1892, 

 Ann. der Physik tend Chem., No. 12, 1892, p. 767. J. t. 



II. Geology and Natueal History. 



1. North American Fossil Mammals. — Volume iv, of the Bul- 

 letin of the American Museum of Natural History, just completed, 

 contains the following important papers on Fossil Mammals : — 



Fossil Mammals of the Wasatch and Wind River beds, (collec- 

 tion of 1891), by H. F. Osborn and J. L. Wortman, covering 6S 



