129 
posing that the flat face of the crystals is (100), one may expect 
the following combinations: (Okl) and (010). 
13. O eliptycznejpolaryzacyi szuiatlaprzechodzqcego, przez 
cialo gazoiue pocht anicijqce, rozunolegle do linij ze- 
zunçtrznego pola magnetycznego . — On the elliptic po¬ 
larization of light transmitted through an absorbing 
gaseous medium, parallel to the lines of an extraneous 
magnetic field. Note de M. LADISLAS NATANSON m. t. 
The magnetic rotation, in gaseous bodies, of the plane of pola¬ 
rization of linearly polarized light was discovered by Kundt and 
Röntgen, and independently by H. Becquerel, in 1879; a very 
complete study of this, the normal Faraday effect in gaseous 
bodies was published by Mr L. H. Si er t sema 1 ). In 1898, how¬ 
ever, the important discovery was made by Messrs M a cal u so and 
Corbino 2 ) that the rotation assumes unusually large values in 
the neighbourhood of an absorption band. The earliest systematic 
measurements of this effect were made for Sodium vapour, in the 
vicinity of the D-lines. by Mr J. J. Hallo 3 ); an extended series of 
experiments is also due to Professor R. W. Wood 4 ) of the Johns 
Hopkins University and another to Mr L. Geiger 5 ) working in 
the Göttingen Laboratory. The theory of the phenomenon was de¬ 
veloped by W. Voigt 6 ), by J. L arm or 7 ), P. Drude 8 ) and 
H. A. Lorentz 9 ). From an exhaustive examination of the agree¬ 
ment existing between observed fact and the various proposed forms 
9 Archives Néerlandaises (2) Vol. 2., p. 291. 1899. 
2 ) Comptes Rendus Vol. 127, p. 548. 1898. 
3 ) Archives Néerlandaises (2) YoJ. 10., p. 148. 1905. 
4 ) Philosophical Magazine (6) Vol. 10., p. 408. 1905; ibidem (6) Yol. 14., 
p. 145. 1907. 
5 ) Annalen der Physik, Bd. 23., p. 758. 1907; ibidem, Bd. 24., p. 597. 1907. 
6 ) Wiedemann's Annalen, Bd. 67, p. 345 1899; ibidem Bd. 68, p. 352. 1899. 
7 ) Aether and Matter, Cambridge 1900. 
% ) Lehrbuch der Optik : 1 Auflage, Leipzig 1900; 2 Auflage, Leipzig 1906. 
9 ) Rapports présentés au Congres Int. de Physique réuni à Paris Yol. III. 
p. 15. 1900. Kon. Akad. v. Wet. te Amsterdam, Proceedings, Meeting of Dec. 
30. 1905. 
1 * 
