054 



PHYSICS, PROGRESS OF, IX 1894. 



observed surfaces are adjusted to equality by 

 varying the .size of apertures through which the 

 light passes from the screens to the surfaces. 

 With small apertures this method admits of 

 comparing different colored lights, since all col- 

 ored lights appear as gray when the intensity is 

 sufficiently feeble. E. S. Terry (' Physical Re- 

 view," March-April) finds that, while the light 

 transmitted by a rotating sectored disk equals 

 the ratio of the total aperture to the entire disk, 

 the effect on the retina is not in this ratio. 

 \Vith mixed light whose elements are of differ- 

 ent luminosity the elements of low luminosity 

 are intercepted most strongly. With a given 

 light the error thus introduced increases as the 

 aperture diminishes, but with ordinary illumi- 

 nants it is negligible when the aperture is more 

 than one half the disk. 



ISpectroscopy. The Rowland concave grat- 

 ing is astigmatic, which is an advantage as re- 

 gards the elimination of dust lines from the 

 spectrum, and the broadening of a star or spark 

 spectrum into a band, but it has hitherto pre- 

 vented the comparison of spectra by simultane- 

 ous observation. Dr. J. L. Lirks, in a pamphlet 

 (Amsterdam, 1894), shows that the comparison 

 may be made, provided the comparison prism 

 or its equivalent, be placed at some distance 

 from the slit, at a point determined by the inter- 

 section of the line joining slit and grating with 

 a line drawn through the focus tangent to a 

 circle whose center bisects the line joining focus 

 and grating. Kayser and Runge (Berlin Acad- 

 emy, December, 1893) have made an exhaustive 

 investigation of the spectra of the elements, dis- 

 covering many new lines, including 14 for tin, 7 

 for antimony, and 22 for bismuth. The same 

 (Wiedemann's "Annalen," May) have attempted 

 to find uniformities in the structure of the me- 

 tallic line spectra, and find that the spectra of 

 the metals investigated may be reconstructed by 

 superposing several equal spectra differing by a 

 constant oscillation frequency. Tin, lead, and 

 arsenic require 3 such spectra, antimony 6, and 

 bismuth 4. Janssen (Paris Academy of Sciences) 

 lias made new observations on the absorption 

 spectrum of oxygen at high temperatures. The 

 heating up to 300 C. was done by gas jets play- 

 ing directly on the tube containing the oxygen, 

 which was 30 feet long. Above 300 the gas was 

 heated by raising to incandescence a platinum 

 spiral by electricity. Temperatures of between 

 SIM) and 900 were thus obtained. Thechief point 

 brought out is the remarkable increase of trans- 

 parency with increase of heat, the spectrum be- 

 coming brighter and extending its limits, espe- 

 cially at the red end. Thomas Ewan (London 

 I loyal Society, June 21) finds that the absorption 

 spectra of very dilute solutions of several copper 

 salts are identical. F. Paschen (Wiedemann's 

 "Annalen." December, 1898) finds that there is 

 no practical difference in the spectrum of a gas 

 heated to 1,000 and the same burned in a Bun- 

 sen (lame. He recognizes three types of light 

 emission: (1) That of the vacuum tube nearly 

 all Luminescence; (2) that of metallic: vapors in 

 the I.unsen flame luminescence with true tem- 

 perature emission ; (3) that of glowing gases 

 entirely due to temperature. Schuster ("Philo- 

 sophical Maga/ine." .June), in a discussion of cer- 

 tain interference phenomena, points out that our 



observations tell us nothing directly of the vi- 

 bration of a luminous body, but only of the dis- 

 turbance in the surrounding medium. The dis- 

 tribution of energy in the resulting spectrum 

 may indicate a property of the medium rather 

 than of the luminous matter. The vibration of 

 the molecule, for instance, may be irregular, but 

 the medium may take up and propagate some 

 vibrations more quickly than others. 



Spectrum Photography. Edes and Valenta 

 (Vienna Academy of Science) have obtained pho- 

 tographs of Bunsen-flame spectra by means of 

 an apparatus that makes exposures of great 

 length possible. A rotating disk of platinum 

 gauze, mounted in a slanting position, dipped into 

 a solution of the salt to be examined and passed 

 at its upper edge through the flame. Prof. S. P. 

 Langley, of the Smithsonian Institution (Paris 

 Academy of Science, Aug. 13), has been able, by 

 a perfected arrangement of the bolometer, and 

 by automatically photographing the movements 

 of the galvanometer needle, to furnish in one 

 hour a complete and accurate record of the infra- 

 red region of the solar spectrum. The experi- 

 ments of Victor Schumann on photography of 

 rays of very short wave length are described in 

 " Naturwissenschaft Rundschau," No. 50. Very 

 high ultraviolet photography has hitherto been 

 interfered with by absorption in the prisms, 

 lenses, and plate, and even in the atmosphere 

 itself. Schumann, by discarding gelatin and 

 using a pure silver- bromide plate, and by exhaust- 

 ing the camera, spectroscope, and spark-tube of 

 air, has added to the known spectrum the re- 

 gion down to 100 micro-millimetres, and has ex- 

 haustively explored the hitherto doubtful region 

 down to 185 micro-millimetres. G. Meyer (Wiede- 

 mann's " Annalen,'' March) has devised a new and 

 ingenious method of photographing the spec- 

 trum of lightning. A diffraction grating ruled 

 on glass is placed in front of the object glass, 

 which is focused for an infinite distance. Sev- 

 eral images of the flash are thus obtained, a cen- 

 tral one from the undiffracted rays, and others 

 corresponding to the different orders of diffrac- 

 tion spectra, the number of images of each order 

 equaling the number of lines in the spectrum. 

 Experiments with the apparatus seem to show a 

 hitherto unobserved line in the lightning spec- 

 trum, at about wave-length 382 micro-milli- 

 metres. 



Polarization. K. E. F. Schmidt, in experi- 

 ments on elliptical polarization by reflection 

 (" Wiedemann's Annalen," May), finds that with 

 glasses of equal refractive indices and different 

 dispersive powers the glass with the higher dis- 

 persion shows the wider range of angle at which 

 ellipticity is observed. G. Moreau ("Annales 

 de Chimie et Physique,'' February) has investi- 

 gated the magneto-rotary power of carbon bi- 

 sulphide in the infrared part of the spectrum, 

 and has succeeded in measuring it between 0'8 

 and 1-4 micro-millimetres, but the absorption of 

 the bisulphide prevented observations at greater 

 wave lengths. 



Percy Frankland ("Chemical NeWs," Jan. 1!) 

 and 2G), in a review of the present state of knowl- 

 edge regarding the dependence of physical qual- 

 ities on atomic arrangement, lays stress on the 

 experiments of Crum Brown and Guye. which 

 show that rotary power is directly dependent 



