There are some interesting phenomena connected with the Zeeman effect which are more easily observed than the effect itself. Thus Cotton[51] found that if we have two Bunsen flames, A and B, coloured by the same salt, the absorption of the light of one by the other is diminished if either is placed between the poles of a magnet: this is at once explained by the Zeeman effect, for the times of vibration of the molecules of the flame in the magnetic field are not the same as those of the other flame, and thus the absorption is diminished. Similar considerations explain the phenomenon observed by Egoroff and Georgiewsky,[52] that the light emitted from a flame in a transverse field is partially polarized in a plane parallel to the magnetic force; and also Righi's[53] observation that if a sodium flame is placed in a longitudinal field between two crossed Nicols, and a ray of white light sent through one of the Nicols, then through the flame, and then through the second Nicol, the amount of light passing through the second Nicol is greater when the field is on than when it is off. Voight and Wiechert (_Wied. Ann._ 67, p. 345) detected the double refraction produced when light travels through a substance exposed to a magnetic field at right angles to the path of the light; this result had been predicted by Voight from theoretical considerations. Jean Becquerel has made some very interesting experiments on the effect of a magnetic field on the fine absorption bands produced by xenotime, a phosphate of yttrium and erbium, and tysonite, a fluoride of cerium, lanthanum and didymium, and has obtained effects which he ascribes to the presence of positive electrons. A very complete account of magneto- and electro-optics is contained in Voight's _Magneto- and Elektro-optik_. FOOTNOTES: [1] _Experimental Researches_, Series 19. [2] _Comptes rendus_, 88, p. 709. [3] _Wied. Ann._ 6, p. 332; 8, p. 278; 10, p. 257. [4] _Wied. Ann._ 23, p. 228; 27, p. 191. [5] _Wied. Ann._ 31, p. 941. [6] _Phil. Trans._, A. 1885, Pt. 11, p. 343. [7] _Wied. Ann._ 26, p. 456. [8] _Phil. Trans._, A. 1895, Pt. 17, p. 621. [9] _Wied. Ann._ 24, p. 161. [10] _Wied. Ann._ 31, p. 970. [11] _Comptes rendus_, 57, p. 670. [12] _Comptes rendus_, 43, p. 529; 44, p. 1209. [13] _Journ. Chem. Soc._ 1884, p. 421; 1886, p. 177; 1887, pp. 362 and 808; 1888, p. 561; 1889, pp. 680 and 750; 1891, p. 981; 1892, p. 800; 1893, pp. 75, 99 and 488. [14] _Wied. Ann._ 44, p. 377. [15] _Wied. Ann._ 43, p. 280. [16] _Zeitschrift f. physikal. Chem._ 11, p. 753. [17] _Phil. Mag._ [5] 3, p. 321. [18] _Ann. de chim. et de phys._ [6] 4, p. 433; 9, p. 65; 10, p. 200. [19] _Wied. Ann._ 23, p. 228; 27, p. 191. [20] _Wied. Ann._ 39, p. 25. [21] _Wied. Ann._ 42, p. 115. [22] _Phil. Mag._ [5] 12, p. 171. [23] _Journ. de Phys._ 1884, p. 360. [24] _Beiblätter zu Wied. Ann._ 1885, p. 275.