1874.] Mr. J. N. Lockyer's Spectroscopic Notes. No. II. 373 



6. The spectroscope supplies us with intermediate stages between these 

 extremes. 



(a) The spectra vary as we pass from the induced current with the 

 jar to the spark without the jar, to the voltaic arc, or to the highest 

 temperature produced by combustion. The change is always in the same 

 direction ; and here, again, the spectrum we obtain from elements in a 

 state of vapour (a spectrum characterized by spaces and bands) is similar 

 to that we obtain from vapours of which the compound nature is un- 

 questioned. 



(ft) At high temperatures, produced by combustion, the vapours of some 

 elements (which give us neither line- nor channelled space-spectra at those 

 temperatures, although we undoubtedly get line-spectra when electricity is 

 employed, as stated in 4) give us a continuous spectrum at the more 

 refrangible end, the less refrangible end being unaffected. 



(y) At ordinary temperatures, in some cases, as in selenium, the more 

 refrangible end is absorbed ; in others the continuous spectrum in the 

 blue is accompanied by 'a continuous spectrum in the red. On the 

 application of heat, the spectrum in the red disappears, that in the blue 

 remains ; and further, as Faraday has shown in his researches on gold- 

 leaf, the masses which absorb in the blue may be isolated from those 

 which absorb in the red. It is well known that many substances known 

 to be compounds in solution give us absorption in the blue or blue and 

 red ; and, also, that the addition of a substance known to be compound 

 (such as water) to substances known to be compound which absorb the 

 blue, superadds an absorption in the red. 



7. In those cases which do not conform to what has been stated the 

 limited range of the visible spectrum must be borne in mind. Thus I have 

 little doubt that the simple gases, at the ordinary conditions of tempera- 

 ture and pressure, have an absorption in the ultra-violet, and that highly 

 compound vapours are often colourless because their absorption is beyond 

 the red, with or without an absorption in the ultra-violet. Glass is a 

 good case in point ; others will certainly suggest themselves as opposed 

 to the opacity of the metals. 



8. If we assume, in accordance with what has been stated, that the 

 various spectra to which I have referred are really due to different mole- 

 cular aggregations, we shall have the following series, going from the 

 more simple to the more complex : 



First stage of complexity 1 Lin tram 



of molecule J 



Second stage Channelled space-spectrum. 



f Continuous absorption at the blue 

 end not reaching to the less refran- 

 gible end. (This absorption may 

 break up into channelled spaces.) 



