Gases under High Pressures. 369 



in this experiment. The limits of the spectrum having remained 

 in this case also the same throughout the whole experiment, we 

 have a proof that the continuous spectrum on which the bright 

 lines stand out really belongs to oxygen. 



This gas, then, is distinguished from hydrogen by the fact that 

 it is in the less refrangible part that the bright lines of its fun- 

 damental spectrum spread out and disappear and only leave a 

 continuous spectrum, while in the case of hydrogen these lines 

 first disappear in the more refrangible part. Moreover it never 

 gave, like hydrogen, an absolutely continuous spectrum without 

 any bright line. Even at still higher pressures than those we 

 have indicated, and with a larger Leyden jar charged by a Holtz's 

 machine, the bright lines remain perfectly distinct, at least in the 

 more refrangible part of the spectrum, starting from the green. 



c. Nitrogen,. 



To investigate the spectrum of nitrogen, the author did not 

 work as before on air, but on pure nitrogen ; for it was more 

 than probable that at high pressures oxygen would exert a dis- 

 turbing action upon his experiments which it could not exert in 

 very rarefied air. 



At low pressures he obtained, as before, a beautiful conti- 

 nuous and fluted spectrum of the first class. At 25 millims. the 

 flutings had already disappeared, except in the green and the 

 blue. As the pressure increases, the less refrangible part of the 

 spectrum becomes more and more obscured until a pressure of 

 260 millims. has been attained ; there then scarcely remains more 

 of the first-class spectrum of nitrogen than the blue and violet 

 parts, which are still fluted, and already there is visible in the green 

 part a bright line belonging to the spectrum of the second class. 

 There are then gradually seen to appear an increasing number 

 of these bright lines ; and towards 500 millims. there is, as it 

 were, a struggle between the two nitrogen-spectra. It is easy 

 to see that they are quite distinct, and that the bright lines of 

 the second have no connexion with the flutings of the first. 

 When this latter has quite disappeared, a certain number of 

 bright lines remain which standout upon a continuous and illu- 

 minated ground. The bright lines first appear in the more re- 

 frangible part, and only last of all in the red. From 600 mil- 

 lims., and especially towards 760 millims., this spectrum is com- 

 plete and very bright : this pressure could never be exceeded with 

 the large RuhmkorfFs coil. 



It is easily seen that the continuous spectrum, serving in this 

 case also as a basis for the bright lines, forms an integral part 

 of the second-class spectrum of nitrogen, by the fact that it stops 

 at exactly the same limits as the bright lines. The author does 



Phil. Mag. S. 4. Vol. 39. No. 262. May 1870. 2 B 



