III. On the ultra-violet spectra of the elements.—Part I. Iron (with a map)

• Published in: Philosophical Transactions of the Royal Society of London
• Format: Article in Journal/Newspaper
• Language: English
• Published: The Royal Society 1883
• Subjects: Cornu; Iceland
• Online Access: http://dx.doi.org/10.1098/rstl.1883.0003; https://royalsocietypublishing.org/doi/pdf/10.1098/rstl.1883.0003

Ångström’s “normal solar spectrum” has served most spectroscopists as a standard of reference for wave-lengths in the visible part of the spectrum. Cornu’s continuation of it, and particularly the map of the iron lines which he used in the construction of it, serves very well for such a standard up to the limit of the solar spectrum, i. e ., to a wave-length 2948 (U). For the region above this we have had to use Mascart’s and Cornu’s wave-lengths of the cadmium lines, and Cornu’s wavelengths of some magnesium lines. The intervals between those lines are, however, too great for any close approximation to the wave-lengths of intervening lines by interpolation, and, moreover, the wave-lengths did not appear to be determined with sufficient precision to serve as a standard, and the lines are ill adapted to that purpose by reason of their diffuse character. For the determination of the wave-lengths of lines in this higher region we have, therefore, been driven to form a standard for ourselves. For this purpose we have chosen the iron spectrum which had been employed by Cornu in the region which he mapped, and seemed to answer the purpose well, both from the number of lines which it presents and their characteristic grouping by which they may easily be recognised by anyone who has once become familiar with them. The wave-lengths of the most prominent lines were determined by means of a Rutherfurd diffraction grating, as detailed below, between the wave-lengths 2948 and 2327; but beyond this there is a remarkable falling off in the intensity of the iron lines, and between wave-lengths 2327 and 2135 (which is near the limit of transparency of Iceland spar) we have preferred to determine the wave-lengths of the prominent copper lines which are numerous and strong in that region. The wave-lengths of a series of lines at short intervals having thus been determined, those of the intervening lines were obtained by interpolation, and the result is shown in the map of the iron spectrum above U which accompanies this paper. The ...