130 RECENT PROGRESS IN OPTICS. 



Through the spectroscope chiefly has been established during the 

 present year the discovery of the new atmospheric element, argon, by 

 Lord Eayleigh and Professor Ramsay (Proc. Eoyal Society, January 

 31, 1895) 1 ; its remarkable property of green fluorescence when the 

 electric spark is passed through it in presence of benzine, by Berthelot 

 and Deslandres (Comptes rendus, June 24, 1895) ; and its association 

 in meteoric iron and various minerals with helium, now proved to be a 

 terrestrial as well as solar element, by Bamsay (Mature, April 4, May 

 16, July 4 and 25, 1895), Crookes, Lockyer, and others. 



With the diffraction spectroscope Eydberg (Wiedemann's Annalen, 

 1893-1894) and Kayser and Bunge (ibid., 1888-1895) have discovered 

 interesting relations among the spectral lines of a large number of 

 terrestrial elements, arranging them into series whose distribution 

 manifests chemical relationship quite analogous to that indicated in 

 Mendelejeff's i>eriodic law. 



By photographing the spectrum of Saturn's rings and noting the 

 relative displacement of the different parts of a spectral line, Keeler 

 (Astrophysical Journal, May 1895, p. 416) has obtained a beautiful 

 direct proof of the meteoric constitution of these rings, a confirmation 

 of the hypothesis put forth by Maxwell in 1859, that the outer portion 

 of the rings must revolve more slowly than the inner portion, and yet 

 not satisfy the conditions of fluidity. His work has been repeated 

 and confirmed by Campbell (ibid., August 1895, p. 127) at the Lick 

 Observatory. 



The spectroheliograph devised by Hale (Astronomy and Astrophys- 

 ics, March, 1893, p. 256) has enabled him to photograph, on any bright 

 day, not only the solar photosphere and spots, but also the chromo- 

 sphere and protuberances. He has made some remarkable attempts 

 with this instrument to photograph the corona without an eclipse, 

 unsuccessfully thus far, but not without promise of future success. 



POLARIZED LIGHT. 



In the domain of polarized light, there have been several noteworthy 

 recent researches. Nichols and Snow (Philosophical Magazine (5), 

 Vol. XXXIII, p. 379) have shown that calcite, though readily trans- 

 parent for the brighter rays of the spectrum, rapidly diminishes in 

 power of transmission for waves of short period, so that for the extreme 

 violet this power is scarcely half so great as for the yellow. The 

 transmissive power of this crystal for the infra-red rays, between the 

 wave-length limits of 1 micron and 5.5 microns, has been investigated 

 with the bolometer by Merritt (Physical Review, May-June 1895, p. 

 424), who reaches the interesting result that the transmission curve for 



1 See also Smithsonian Contributions to Knowledge, Vol. XXIX, where is published 

 the original memoir announcing the discovery of argon, for which Lord Eayleigh 

 and Professor Ramsay were awarded thelirst prize of $10,000, in the Hodgkins Fund 

 Prize competition of the Smithsonian Institution. — Editor. 



