Constitution of H and K lines of Solar Spectrum. 525 



such distances from the electrodes during the time of dura- 

 tion of: the, discharges would demand a prodigious velocity of 

 the particles. I have made a careful study of the influence 

 of metallic electrodes in the tubes employed by me and find 

 no spectra due to them. 



In order to determine whether the walls of the glass tubes 

 could give lines due to calcium, I first placed aluminium ter- 

 minals on a sheet of glass of the same kind as that from 

 which the Geissler tubes were made ; and having placed the 

 glass against the slit of the spectroscope, I passed powerful 

 discharges of the same nature and energy as were employed 

 in the study of the spectra of gases. The glass was badly 

 corroded along the path of the discharge, showing the same 

 corrosion which was observed in the capillary of the glass 

 Geissler tubes. 



No continuous spectrum was observed and no calcium 

 lines. Similar discharges were passed through fifty ohms of 

 No. 36 iron wire ; the wire was barely raised to a dull red 

 heat. A photograph was taken of ten centimetres of such 

 wire, illuminated by the discharge from a Geissler tube 

 placed in the same electrical circuit. The photograph showed 

 the wire intact at the moment of the illumination of the tube. 

 It took time to communicate sufficient heat to melt the wire. 

 On the same photograph was shown the subsequent melting 

 of the wire. That is the wire is seen intact, and also the two 

 ends of the wire contorted and burning. If the walls of the 

 capillary of the glass vessels are heated to incandescence the 

 time element must be large, for the gas must first be heated 

 by the discharge and then the walls of the glass by conduc- 

 tion and radiation. Thermodynamic considerations make it 

 impossible that the walls of the glass vessels are heated to 

 incandescence ; moreover, Wiedemann *" has shown that the 

 heat of electrical discharges in Geissler tubes has been much 

 exaggerated. A photograph was taken of the light from 

 a Geissler tube by means of a rapidly revolving mirror. 

 Beside the tube and in the same circuit was a spark-gap 

 between magnesium terminals. The duration of the light of 

 the Geissler tube was one-fourth of that of the spark between 

 the magnesium terminals in air. There was absolutely no 

 duration of the light of the Geissler tube due to a supposable 

 incandescence of the glass. The light in the Geissler tube 

 arising from powerful disruptive discharges is the strongest 

 and most instantaneous light which has been obtained, and 

 would be useful in the study of rapid motions. 



If the glass is not vaporized by the discharges I have 

 * Wied. Ann vi. (1878). 

 Phil. Mag. S. 6. Vol. 5. No. 29. May 1903. 2 N 



