of the H and K lines of the Solar Spectrum. 527 



solar spectrum, and also with the gaseous lines I have ob- 

 tained in rarefied hydrogen*. Terminals of aluminium, 

 copper, iron, tin, magnesium, show these lines faintly. The 

 noble metals, which are least affected by the electric discharge 

 and which are therefore used for nonoxidizable contact in 

 electric apparatus, give these lines strongly. Is it not pro- 

 bable that when the electric discharges volatilize to a high 

 degree the metallic terminals, electric discharge prefers a 

 passage through the metallic vapour, and does not sufficiently 

 heat the air to bring out certain air lines ? The method of 

 sifting out air lines from metallic spectra by observing the 

 lines which are apparently common to these spectra, and 

 setting down such lines as air lines, is a fallacious method. 

 Silicon is not easily volatilizable, and certain important 

 groups of lines attributed to that metal, obtained by the use 

 of the spark in air, may be atmospheric lines. I have ob- 

 tained traces of such lines which seem to coincide with the 

 gaseous lines I obtained with rarefied hydrogen in quartz 

 tubes by employing water electrodes. These electrodes were 

 made as follows : — two iridium terminals were placed on 

 pieces of kiln-dried wood four inches apart. The condenser 

 spark could leap only one inch. The wood was wrapped with 

 cotton, inclosing the metallic terminals, around the cotton 

 was wrapped chamois skin ; the clear space between the ends 

 of the wood thus protected was half an inch. The terminals 

 thus prepared were soaked in distilled water. A very powerful 

 spark was thus obtained in air which was entirely free from 

 metallic lines. With these terminals it is undoubtedly true 

 that the water-vapour conducted the main body of the dis- 

 charge, just as the metallic vapour does in dry air. The 

 edges of this spark show a strong red tint, and give the line- 

 spectrum of hydrogen. The centre of the spark is of a 

 brilliant whiteness. Strong bands appear in the position of 

 the reversed lines which I have obtained with rarefied hydro- 

 gen in the quartz tubes. I therefore believe that these lines 

 are gaseous lines. 



I believe that these lines, and also the great H.H. lines of 

 the solar spectrum, are due to oxygen. At very high tempe- 

 ratures the oxygen atom set free from the salts of calcium 

 and its allied metals is free to vibrate in its own periods. It 

 does not seem improbable that many lines attributed to metals 

 may be oxygen lines ; the metal releasing its hold of the 

 oxygen atom at very high temperatures. 



* Compare with paper " On the Constitution of the Electric Spark." 

 Arthur Schuster, F.R.S., and Gustav Hemsalech, Phil. Trans. Roy, Soc. 

 vol. cxciii. series A. 



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