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VI. The Sijectra of Neon^ Krypton and Xenon. 
By E. C. C. Baly, Lecturer on Spectroscopy in University College, London. 
Communicated hy Sir AVilliam Bams ay, K.C.B., F.R.S. 
Eeceived June 12,—Read June 18, 1903. 
Soon after the discovery of the new gases, neon, krypton and xenon, by Sir William 
Ramsay and Dr, Thayers, 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 vutli the help of the grating far more 
accurate results than v-as possible from measurements of the photographs taken with 
the prism ajiparatus. Since the commencement of this work three series of measure¬ 
ments have been published, one hy Runge of certain lines in the krypton spectra, 
and two hy Liveing and Deavar of the lines in the spectra of the light t and lieavy | 
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 Dem'Ar’s measurements also are only given to the nearest 
Angstrhm unit. The publication of these tables of v^ave-lengths emphasised still 
more strongly m 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 C|ualitative Avork, is to he found in their reliability, especially at 
the present time Avhen so much Avork is being done upon spectral series. It is 
difficult to assess the accuracy Avhich may be claimed for the measurements given 
heloAv, hut, judging from the Amines obtained for certain lines common to the spectra, 
the probable error may be estimated to be less than 0'03 Angstrom unit. The 
specimens of the gases used A\mre not spectroscopically pure, the neon contained 
traces of helium, Avhile 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 AAmre measured in due course ; the Avave-lengths found 
* ‘ Astrophys. Jcurn.,’ vol. 10, p. 73, 1899. 
t ‘Roy. Soc. Proc.,’ a'oI. 67, p. 467, 1900. 
I ‘Roy. Boe. Proc.,’ vol. 68, p. 389, 1901. 
A"OL. CCII.—A 3.51. 11.11.03 
