v.] TELLURIC LINES. 65 



at Alta Vista, another station, 10,702 feet high, the H lines had 

 lost their nebulosity and the spectrum was visible beyond H to 

 three times the distance of its bars asunder. 



Singularly enough, Brewster l himself, in 1859, when the truth 

 of his view of the solar origin of those Fraunhofer lines which 

 had not been traced to atmospheric absorption was being con- 

 firmed on all sides, appeared less satisfied with it, and Dr. 

 Gladstone, who was now associated with him, endeavoured to 

 show that they also might have a telluric origin. They suggested 

 the possibility of the lines being due to interference, 2 as Brewster 

 had observed analogous lines and bands in portions of decom- 

 posed glass consisting of numerous films. But not being quite 

 satisfied with this they attempted to ascertain whether the 

 earth's atmosphere had any share in their production. Dr. Glad- 

 stone therefore, in 1859, 3 examined the light of the lighthouse 

 at Beachy .Head from Shoreham and Worthing (twenty-five 

 and twenty-seven miles respectively), expecting to find the 

 Fraunhofer lines. The only result of this observation, however, 

 was that the spectrum terminated at c and F, and no dark lines 

 appeared, and they concluded, therefore, that the origin of those 

 fixed lines must still be considered an undecided question. 



Hoping to obtain some confirmation of the telluric origin of 

 the variable lines of the solar spectrum, Dr. Gladstone, in 1861, 

 compared them with the bright lines emitted by the different 

 constituents of the atmosphere when sufficiently heated. 4 As 

 data for this comparison, he took Angstrom's maps of the 

 spectra of oxygen, nitrogen, hydrogen, carbonic acid, &c., ob- 

 tained, by means of an electric spark, and Plucker's maps of 

 the spectra of the same and other gases, in Geissler tubes. To 

 obtain the spectrum of aqueous vapour he employed the 

 oxyhydrogen flame, and of carbonic acid, a flame of carbonic 

 oxide. 



1 Phil. Trans. 1860, part i. pp. 157-159. 2 Ibid. p. 159, note. 



3 Ibid. p. 159. 4 Proc. Roij. 8oc. Jiine 20th, 1861. 



F 



