[mclexxax-petrie] spectra OF HELIUM, ETC. 21 



formed by the disruption of carbon atoms. This conclusion fits in 

 with theory for, as is well known, the series for hydrogen atoms 



whose frequencies are given by j'^N (l — -^) consists oi the wave- 

 lengths X=1216 Â.U., X = 1026 Â.U., X = 972 Â.U., etc. Regarding 

 the wave-length X = 1086.1 Â.U. Lyman has expressed the opinion 

 that when he obtained this wave-length in the sprectum of helium 

 it did not originate in helium atoms but in the atoms of some impurity 

 present in the helium used by him. The table shows, however, that 

 this wave-length was obtained by us with fair intensity in the spectrum 

 of helium, but not in the spectrum of hydrogen or in that of the 

 vacuum carbon arc. It was obtained by Millikan also with his "hot" 

 carbon sparks. It seems clear, then, that the wave-length obtained 

 by us at or near X= 1085.2 A.U. and by Millikan at X = 1085.3 Â.U. 

 originated in helium atoms. In the case of Millikan's result this 

 conclusion could lead again to the view that the helium had its origin 

 in the disrupted carbon atoms. As to the wave-length X = 1026 A.U., 

 it will be noted "that while it was not obtained by Millikan in this 

 spectra of carbon sparks, it was obtained by us in the spectrum of the 

 spark discharge in helium and in that gas only. Lyman states that 

 the wave-length X-=1026 Â.U. is usually present on his plates of the 

 spectrum of helium, and that he has also found it in the spectrum of 

 hydrogen. This would go to show that radiation of a wave-length 

 close to X = 1026 Â.U. is obtainable from helium as well as from 

 hydrogen atoms. The indications are, however, that it is easier to 

 obtain a photographic record of the wave-length with helium than it 

 is with hydrogen. The conclusion that this wave-length is obtainable 

 with helium, as well as with hydrogen, is in accordance with what 

 would be expected on the basis of the frequency formulae for these 

 two gases given above. It is not clear, however, why Millikan did 

 not obtain a wave-length at or near X = 1026 A.U. in his spectra of 

 the carbon spark, especially when he obtained the wave-lengths 

 X = 1215.7 A.U. and X = 1085.3 Â.U. with fair intensities. 



As no wave-lengths were obtained by us in the spectra of helium 

 and hydrogen below X = 1020.9 Â.U. we have no material available 

 to contribute anything of value concerning the origin of the wave- 

 lengths X = 992 A.U. and X = 972 A.U. Lyman^ has expressed the 

 opinion that these wavelengths, when obtained in the spectra of 

 helium, were really due to an impurity which, in the case of X = 972 A.U. 



1 Lyman, Nature, VoL 104, p. 314, Nov. 20. 1919. Fricke & Lyman, Phil. 

 Mag., VoL 41, p. 814, 1921. Lyman, Nature, VoL 104, p. 565, Jan. 29, 1920. 



