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 A more extended study of the behaviour of the spectroscopic lines has afforded examples in which the effects produced by a magnet are more complicated than those we have described, indeed the simple cases are much less numerous than the more complex. Thus Preston47 and Cornu48 have shown that under the action of a transverse magnetic field one of the D lines splits up into four, and the other into six lines; Preston has given many other examples of these quartets and sextets, and has shown that the change in the frequency, which, according to the simple theory indicated, should be the same for all lines, actually varies considerably from one line to another, many lines showing no appreciable displacement. The splitting up of a single line into a quartet or sextet indicates, from the point of view of the ion theory, that the line must have its origin in a system consisting of more than one ion. A single ion having only three degrees of freedom can only have three periods. When there is no magnetic force acting on the ion these periods are equal, but though under the action of a magnetic force they are separated, their number cannot be increased. When therefore we get four or more lines, the inference is that the system giving the lines must have at least four degrees of freedom, and therefore must consist of more than one ion. The theory of a system of ions mutually influencing each other shows, as we should expect, that the effects are more complex than in the case of a single ion, and that the change in the frequency is not necessarily the same for all systems (see J. J. Thomson, Proc. Camb. Phil. Soc. 13, p. 39). Preston49 and Runge and Paschen have proved that, in some cases at any rate, the change in the frequency of the different lines is of such a character that they can be grouped into series such that each line in the series has the same change in frequency for the same magnetic force, and, moreover, that homologous lines in the spectra of different metals belonging to the same group have the same change in frequency.

A very remarkable case of the Zeeman effect has been discovered by H. Becquerel and Deslandres (Comptes rendus, 127, p. 18). They found lines in iron when the most deflected components are those polarized in the plane at right angles to the magnetic force. On the simple theory the light polarized in this way is not affected. Thus the behaviour of the spectrum in the magnetic field promises to throw great light on the nature of radiation, and perhaps on the constitution of the elements. The study of these effects has been greatly facilitated by the invention by Michelson50 of the echelon spectroscope.

There are some interesting phenomena connected with the Zeeman effect which are more easily observed than the effect itself. Thus Cotton51 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’s53 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.

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. 25 Messungen über d. Kerr’sche Erscheinung. Inaugural Dissert. Leiden, 1893. 26 Phil. Mag. [5] 5, p. 161. 27 ''Phil. Mag.'' [3] 28, p. 469. 28 ''Die magn. Drehung'' d. Polarisationsebene des Lichts, Halle, 1863. 29 Electricity and Magnetism, chap. xxi. 30 ''Phil. Trans.'' 1880 (2), p. 691. 31 Phil. Mag. (5) 11, p. 254, 1881. 32 ''Arch. Néerl.'' 19, p. 123. 33 ''Wied. Ann.'' 23, p. 493; 67, p. 345. 34 ''Wied. Ann.'' 24, p. 119. 35 ''Wied. Beiblätter'', 8, p. 869. 36 Comptes rendus, 108, p. 510. 37 ''Phil. Trans.'' 182, A. p. 371, 1892; Physical Optics, p. 393. 38 ''Wied. Ann.'' 46, p. 71; 47, p. 345; 48, p. 740; 50, p. 722. 39 ''Wied. Ann.'' 46, p.353; 48, p. 122; 49, p. 690. 40 Recent Researches, p. 489 et seq. 41 Phil. Trans., A. 1897, p. 89. 42 ''Brit. Assoc. Report'', 1893. 43 Comptes rendus, 127, p. 548. 44 ''Bull. de l’Acad. des Sciences Belg.'' (3) 9, pp. 327, 381, 1885; 12 p. 30, 1886. 45 Communications from the Physical Laboratory, Leiden, No. 33, 1896; Phil. Mag. 43, p. 226; 44, pp. 55 and 255; and 45, p. 197. 46 ''Arch. Néerl.'' 25, p. 190. 47 Phil. Mag. 45, p. 325; 47, p. 165. 48 Comptes rendus, 126, p. 181. 49 ''Phil. Mag.'' 46, p. 187. 50 ''Phil. Mag.'' 45, p. 348. 51 Comptes rendus, 125, p. 865. 52 Comptes rendus, pp. 748 and 949, 1897. 53 Comptes rendus, 127, p. 216; 128, p. 45.

MAGNOLIA, the typical genus of the botanical order Magnoliaceae, named after Pierre Magnol (1638–1715), professor of medicine and botany at Montpellier. It contains about twenty species, distributed in Japan, China and the Himalayas, as well as in North America.

Magnolias are trees or shrubs with deciduous or rarely evergreen foliage. They bear conspicuous and often large, fragrant, white, rose or purple flowers. The sepals are three in number, the petals six to twelve, in two to four series of three in each, the stamens and carpels being numerous. The fruit consists of a number of follicles which are borne on a more or less conical receptacle, and dehisce along the outer edge to allow the scarlet or brown seeds to escape; the seeds however remain suspended by a long slender thread (the funicle). Of the old-world species, the earliest in cultivation appears to have been M. Yulan (or M. conspicua) of China, of which the buds were preserved, as well as used medicinally and to season rice; together with the greenhouse species, M. fuscata, it was transported to Europe in 1789, and thence to North America, and is now cultivated in the Middle States. There are many fine forms of M. conspicua, the best being Soulangeana, white tinted with purple, Lenné and stricta. Of the Japanese magnolias, M. Kobus and the purple-flowered M. obovata were met with by Kaempfer in 1690, and were introduced into England in 1709 and 1804 respectively. M. pumila, the dwarf magnolia, from the mountains of Amboyna, is nearly evergreen, and bears deliciously scented flowers; it was introduced in 1786. The Indian species are three in number, M. globosa, allied to M. conspicua of Japan, M. sphenocarpa, and, the most magnificent of all magnolias, M. Campbellii, which forms a conspicuous feature in the scenery and vegetation of Darjeeling. It was discovered by Dr Griffith in Bhutan, and is a large forest tree, abounding on the outer ranges of Sikkim, 80 to 150 ft. high, and from 6 to 12 ft. in girth. The flowers are 6 to 10 in. across, appearing before the leaves, and vary from white to a deep rose colour.

The first of the American species brought to Europe (in 1688 by John Banister) was M. glauca, a beautiful evergreen species about 15 ft. high with obtuse leathery leaves, blue-green above, silvery underneath, and globular flowers varying from creamy white to pale yellow with age. It is found in low situations near the sea from Massachusetts to Louisiana—more especially in New Jersey and the Carolinas. M. acuminata, the so-called “cucumber tree,” from the resemblance of the young fruits to small cucumbers, ranges from Pennsylvania to Carolina. The