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Mr. E. C. C. Baly. [June 12, 



The Spectra of Neon, Krypton, and Xenon." By E. C. C. BALY, 

 Lecturer on Spectroscopy in University College, London. 

 Communicated by Sir WILLIAM EAMSAY, K.C.B., F.K.S. 

 Eeceivecl June 12, Eead June 18, 1903. 



(Abstract.) 



The gases were illuminated by the passage of the discharge from an 

 induction coil through them under reduced pressures. Vacuum tubes 

 were filled with each one of them, and the glowing gas in a capillary 

 portion was examined " end on " through a quartz window. Con- 

 siderable difficulty was experienced in the use of the vacuum tubes, 

 owing to the rapid absorption of the gas by the electrodes when the 

 electric current was kept passing for long periods. It was found 

 that when the gases were quite pure, and free from any diatomic 

 impurities, the aluminium electrodes were readily volatilised, an 

 aluminium mirror being formed upon the immediately surrounding 

 walls of the tube ; at the same time the electrodes became very hot 

 and it was necessary to make them of very stout wire, e.g., No. 12 

 B.W.G. Special care had to be taken in making each individual 

 electrode so as to enable it to withstand the disintegrating action of 

 the discharge. The unusual heating of the electrodes gave rise to 

 considerable trouble on account of the large quantities of hydrogen 

 evolved from them ; it is a common experience to anyone, when filling 

 a new vacuum tube, to find a quantity of hydrogen given out by the 

 electrodes ; this hydrogen, as is well known, may be readily removed 

 by further exhaustion. If, however, into a tube from which this 

 hydrogen has been removed a small quantity of one of the monatomic 

 gases be introduced, a further large quantity of hydrogen is evolved 

 from the electrodes. Every trace of this second quantity of hydrogen 

 must be removed before the tube can be depended upon ; it is necessary 

 to thoroughly wash out the tube by repeated admission of argon and 

 re-exhaustion. 



The measurements were all made upon photographs taken with a 

 Eowland concave grating of 10-foot radius and 14,438 lines to the 

 inch ; the first three orders of spectra were employed and nearly all 

 the chief lines were measured in two orders. As far as can be 

 estimated by the coincidences between the different spectra, the 

 probable error is less than 0'03 Angstrom unit. The spectra 

 are all composed of bright lines and are absolutely characteristic 

 in each case. While neon possesses only one spectrum, krypton 

 and xenon both have two, one being given when the ordinary 

 discharge is passed and the other when a Leyden jar and spark 

 gap are placed in the circuit; this second spectrum is much more 



