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LTV . On the Gaseous Constitution of the H and K lines of 

 the Solar Spectrum, together with a Discussion of Reversed 

 Gaseous Lines. By John Trowbridge*. 

 [Plate XIII.] 



I DESCRIBED in the Phil. Mag. July 1902 and Feb. 

 1903 the discovery of reversed lines in the spectra of 

 gases, when the latter are submitted to powerful disruptive 

 discharges. 



In this paper I shall show that the continuous spectrum 

 observed when glass tubes are employed is not due to the 

 incandescence of the Avails of the tubes ; and also that the 

 lines obtained by me which apparently coincide with calcium 

 lines at wave-lengths 4227 and 3933 ? 3968 are not due to 

 calcium but are gaseous lines. The group of H and K lines, 

 therefore, of the solar spectrum, although being doubtless a 

 composite spectrum, has a strong basis of gaseous lines. 

 This seems more than reasonable when we consider that the 

 solar protuberances are observed through these lines ; and 

 when we also take into account the rarefied nature of the 

 gas and the improbability of a metallic vapour like that of 

 calcium being projected so far from the limb of the sun. 



It seemed necessary, in the progress of my work, to deter- 

 mine to what degree metallic electrodes influence the spectra 

 in Greissler tubes of the dimensions I have employed. TThen 

 long and powerful sparks are produced in air the metallic 

 lines disappear at a distance of less than two inches from the 

 terminals. The photograph, therefore, of the spectrum pro- 

 duced by a spark of three or four feet in length shows 

 nothing but air-lines when the slit of the spectroscope re- 

 ceives the light from the middle of the spark. This is true 

 even when sparks of eight inches are examined. The most 

 effective way, therefore, of sifting out air-lines from metallic 

 spectra is to employ long and powerful sparks. At one time 

 I believed that the oscillatory nature of the discharge in- 

 fluenced the nature of the spectra. I am now of the opinion 

 that self-induction acts merely by diminishing the instan- 

 taneous energy of the discharge. 



In the present paper I shall confine my attention mainly 

 to the immediate region of the H and K Jines of the solar 

 spectrum. 



In Geissler tubes, having capillaries not less than two 

 inches in length, the terminals being three and a half or four 

 inches apart, no metallic lines were observed under the con- 

 ditions of my work. Indeed, to produce metallic spectra at 

 * Communicated by the Author. 



