Gases of Atmospheric Air, and their Spectra. 213 



that of the tube, the former being admitted through one-half 

 of the slit, and the latter through the other half. 



The xenon spectrum is characterized by a group of four 

 conspicuous orange rajs of about equal intensities, a group of 

 very bright green rajs of which two are especially conspicu- 

 ous, and several very bright blue rays. The only list of xenon 

 rajs we have seen is that published by Erdmann, with which 

 our list does not present any close agreement except as to the 

 strongest green lines. The number of xenon rays we have 

 observed is very considerable, and some of them lie very near 

 to rajs of the second spectrum of hjdrogen, but inasmuch as 

 these rajs are more conspicuous with a jar in circuit than with- 

 out, which is not the character of the second spectrum of 

 hydrogen, and, moreover, many of the brightest of the hjdro- 

 gen rays are absent from the spectrum of the tubes, we con- 

 clude that these rays are not due to hjdrogen. Certain rays, 

 which we have tabulated separately, have been as yet observed 

 in only one tube : they include a verj strong ultra-violet raj 

 of unknown origin, and due either to some substance other 

 than xenon, or to some condition of the tube which has not 

 been repeated in the other tubes. 



Our krypton rajs agree much more closely with Runge's 

 list, but outnumber his very considerably, as might be expected 

 when prisms were used instead of a grating. Prisms, of course, 

 cannot compete with gratings in the accuracy of wave-length 

 determinations. We think that the krypton used by Runge 

 must have contained some xenon, and that the rays for which 

 he gives the wave lengths 5419*38, 5292*37, and 4844-58 were 

 really due to xenon, as they are three of the strongest rays 

 emitted by our xenon tubes, and are weak in, and in some 

 cases absent from, the spectra of our krypton tubes. 



Tables of the approximate Wave-lengths of Xenon and Krypton 



Rays. 



Rays observed only with a Leyden jar in circuit have a * 

 prefixed, those observed only when no Leyden jar was in cir- 

 cuit have a f prefixed. 



The intensities indicated are approximately those of the rays 

 when a jar is in circuit, except in the case of the two rays to 

 which a f is prefixed, which are not seen when a jar is in cir- 

 cuit. Rays which are equally intense whether a jar is in 

 circuit or not have a || prefixed to the number indicating their 

 intensities ; those which are less intense with a jar than with- 

 out have a < prefixed to the number expressing their intensi- 

 ties. The rest are, in general, decidedly more intense with a 

 jar than without. 



