368 



SCIENCE. 



[N. S. Vol. XXII. No. 560. 



(1832) and MacCullagh (1837) gave sharper 

 statements to these phenomena. Equations 

 were advanced by Cauchy (1836, et seq.) 

 for isotropic bodies, and later with greater 

 detail by Rayleigh (1872), Ketteler (1875, 

 et seq.), Drude (1887, et seq.) and others. 

 Jamin (1847, 1848) devised the first ex- 

 periments of requisite precision and found 

 them in close agreement with Cauchy 's the- 

 ory. Kundt (1888) more recently investi- 

 gated the refraction of metallic prisms. 



Anomalous dispersion was discovered by 

 Christiansen in 1870, and studied by 

 Kundt (1871, etseq.). Sellmeyer's (1872) 

 powerful and flexible theory of dispersion 

 was extended to include absorption effects 

 by Helmholtz (1874), with greater detail 

 by Ketteler (1879, et seq.), and from a dif- 

 ferent point of view by Kelvin (1885). 

 The electromagnetic theory lends itself par- 

 ticularly well to the same phenomena, and 

 Kolazek (1887, 1888), Goldhammer (1892), 

 Helmholtz (1892), Drude (1893) and 

 others instanced its adaptation with suc- 

 cess. 



PHOTOMETRY, FLUORESCENCE, PHOTOCHEM- 

 ISTRY. 



The cosine law of Lambert (1760) has 

 since been interpreted in a way satisfying 

 modern requirements by Fourier (1817, 

 1824) and by Lommel (1880). Among 

 new resources for the experimentalist the 

 spectrophotometer, the Lummer-Brodhun 

 photometer (1889) and Rood's flicker pho- 

 tometer (1893, 1899) should be mentioned. 



Fluorescence, though ingeniously treated 

 by Herschel (1845, 1853) and Brewster 

 (1846, et seq.), was virtually created in its 

 philosophical aspects by Stokes in his great 

 papers (1852, et seq.) on the subject. In 

 recent years Lommel (1877) made note- 

 worthy contributions. Phosphorescence 

 has engaged the attention of E. Becquerel 

 (1859), among others. 



The laws of photochemistry are in large 



measure due to Bunsen and Roscoe (1857, 

 1862). The practical development of pho- 

 tography from its beginnings with Da- 

 guerre (1829, 1838) and Niepce and Fox- 

 Talbot (1839), to its final improvement by 

 Maddox (1871) with the introduction of 

 the dry plate, is familiar to all. Vogel's 

 (1873) discovery of appropriate sensitizers 

 for different colors has added new re- 

 sources to the already invaluable applica- 

 tion of photography to spectroscopy. 



INTERFERENCE. 



The colors of thin plates treated succes- 

 sively by Boyle (1663), Hooke (1665), and 

 more particularly by Newton (1672, 'Op- 

 tiks, ' 1704), became in the hands of Young 

 (1802) the means of framing an adequate 

 theory of light. Young also discovered the 

 colors of mixed plates and was cognizant 

 of loss of half a wave-length on reflection 

 from the denser medium. Fresnel (1815) 

 gave an independent explanation of New- 

 ton's colors in terms of interference, de- 

 vising for further evidence, his double mir- 

 rors (1816), his biprism (1819) and even- 

 tually the triple mirror (1820). Billet's 

 plates and split lens (1858) belong to the 

 same classical order, as do also Lloyd's 

 (1837) and Haidinger's (1849) interfer- 

 ences. Brewster's (1817) observation of 

 interference in case of thick plates cul- 

 minated in the hands of Jamin (1856, 

 1857) in the useful interferometer. The 

 scope of this apparatus was immensely ad- 

 vanced by the famous device of Michelson 

 (1881, 1882), which has now become a fun- 

 damental instrument of research. Michel- 

 son's determination of the length of the 

 meter in terms of the wave-length of light 

 with astounding accu^racy is a mere ex- 

 ample of its accomplishments. 



Wiener (1890) in his discovery of the 

 stationary light wave introduced an entire- 

 ly new interference phenomenon. The 

 method was successfully applied to color 



