Geology and Mineralogy. 495 



aluminum chloride by Nilson and Pettersson, which led them to 

 give to this substance the formula A1C1 3 .— Ber. Berl. Chem. Ges., 

 xxi, 687-701, March, 1888. G. f. b. 



4. Application of interference fringes to Spectrum Analysis. — 

 Hermann Ebert, working in the same direction as Professor 

 Michelson, shows that the method of interference can be used to 

 measure wave-lengths and to detect slight changes in refrangi- 

 bility of spectral lines. In the latter respect he believes that the 

 method is far more delicate than the ordinary spectroriietric 

 methods. One can measure displacements of fringes amounting 

 to y 1 ^ of the breadth of the fringes, or -g-i-g- of the distance of the 

 components of the sodium line, or a change in the velocity of 

 light of f of a kilometer. — Ann. der Physik tend Chemie, pp. 39- 

 90, No. 5, 1888. J. t. 



5. Penetration of light beneath the surface of water. — In con- 

 tinuation of his work upon this subject, M. F. A. Forel finds that, 

 for chloride of silver, the limits of absolute darkness range from 

 45 meters in July to 110 in March. The variations in these lim- 

 its correspond closely with those for visibility. The water of 

 Lake Geneva, in which these experiments were tried, is more 

 limpid in winter than in summer. — Comptes Bendus, April 3, p. 

 1004. j. t. 



6. Velocity of Sound. — MM. J. Violle and Th. Vautier con- 

 clude from their researches that the velocity of a sound wave 

 diminishes with its intensity ; and that the pitch of the sound has 

 no influence on the velocity of the wave.— Comptes Bendus, April 

 3, p. 1003. j. t. 



7. Magnetism and dia.magnetism of gases. — At a meeting of 

 the Physical Society held in Berlin, March 16, Helmholtz de- 

 scribed a method of measurement due to Professor Topler, of 

 Dresden. An index drop of petroleum is placed in a glass tube 

 bent at a very obtuse angle; on one side of the index is the gas 

 which is to be investigated, and on the other side is atmospheric 

 air. When placed between the poles of a powerful electro-mag- 

 net, the index is moved according as the gas is more or less 

 strongly attracted than the air; the amount of displacement is 

 measured by a microscope. The delicacy of the method is ex- 

 tremely great. It was observed that oxygen is most magnetic, 

 then come air and nitric oxide ; nitrogen, hydrogen, carbonic 

 oxide, carbonic acid gas and nitrous oxide, on the other hand, 

 are diamagnetic. The method can also be employed for the de- 

 termination of the pressure of small columns of gases. — Nature, 

 April 12, 1888. j. t. 



II. Geology and Minekalogy. 



1. Three Cruises of the United States Coast and Geodetic 

 Survey Steamer Blake in the Gidf of Mexico, in the Caribbean 

 Sea, and along the Atlantic Coast of the United States ; by 

 Alexander Agassiz. In two volumes of 314 and 220 pages 

 8vo, with numerous maps, plates and figures in the text. Boston 



