VI. The spectra of neon, krypton and xenon

Abstract

Soon after the discovery of the new gases, neon, krypton and xenon, by Sir William Ramsay and Dr. Travers, in 1898, measurements were made of the lines of their emission spectra by means of a large prism spectrograph in University College. In view of the fact that a large Rowland grating apparatus was at that time in process of erection, it did not appear worth while to publish this first series of measurements, as I was in hopes of being able to obtain with the help of the grating far more accurate results than was possible from measurements of the photographs taken with the prism apparatus. Since the commencement of this work three series of measurements have been published, one by Runge of certain lines in the krypton spectra, and two by Liveing and Dewar of the lines in the spectra of the light and heavy constituents of atmospheric air respectively. All these measurements contain only the principal lines and, moreover, extend only a short distance into the ultra-violet region. Liveing and Dewar’s measurements also are only given to the nearest Ångström unit. The publication of these tables of wave-lengths emphasised still more strongly in my mind the necessity for making the measurements with as high a degree of accuracy as possible, for the chief value of tables of such constants beyond the purpose of simple qualitative work, is to be found in their reliability, especially at the present time when so much work is being done upon spectral series. It is difficult to assess the accuracy which may be claimed for the measurements given below, but, judging from the values obtained for certain lines common to the spectra, the probable error may be estimated to be less than ± 0.03 Ångström unit. The specimens of the gases used were not spectroscopically pure, the neon contained traces of helium, while the krypton and xenon contained very small traces of argon; the more important spectrum lines of these impurities were generally to be found upon the photographs and were measured in due course; the wave-lengths found showed an extremely satisfactory agreement with Runge and Paschen’s or Kayser’s determinations. In apology for the length of time taken over the work I must urge certain unavoidable delays, of which the chief ones were due to the long exposures necessary to obtain the weaker lines and the short lives of the vacuum tubes employed; as will be explained below, these tubes will not withstand the long continued action of the electric discharge and therefore they require to be frequently refilled. One of the greatest delays arose from the fact that at one time the whole supply of xenon was used up arid it became necessary to prepare a further quantity to finish this work. I take this opportunity of thanking Sir William Ramsay for his great kindness in undertaking this for me.