On the Action of the Violet and Ultra-violet Invisible Light. 115 



the light thus obtained to penetrate into the fluorescent bodies, 

 proved, at least, not the contrary of my supposition. I ascribe 

 the cause of the partially slight success to the circumstance, that 

 I possessed no blue and violet glasses of sufficient purity, which 

 on that account allowed fewer of the more intensely acting rays 

 to pass through. At last the violet light occurred to me, which 

 results in the so-called electric egg when it is exhausted of air. 

 I tried its action on fluorescent bodies, and was delighted to see 

 that it produced some of the appearances described by Stokes, 

 with a splendour which 1 have never seen with the most beautiful 

 experiment by means of the spectrum. Paper on which a design 

 had been made with a solution of sulphate of quinine, showed 

 at a distance of ten to twelve feet from the oval receiver in the 

 dark chamber, all the details of the design in the most beautiful 

 white on a deep violet ground. Ruhmkorff's induction appa- 

 ratus is extremely convenient for the production of the electric 

 light in the receiver, when the latter is almost exhausted of air. 

 The appearance is so striking, as to lead to the belief that the 

 writing or design on the paper is itself shining and sparkling. 



Hence, in my opinion, it follows, — 1. That the violet light 

 produced in vacuo is mixed with a large quantity of invisible 

 ultra-violet rays. 2. That out of the ultra-violet rays of the so- 

 called northern light invisible to the naked eye, there results by 

 interference in fluorescent bodies a quantity of visible light, and 

 that therefore this light, reflected from the surface of the paper 

 which has been marked with quinine solution, appears brighter 

 than direct light; that therefore, out of the ultra-violet light 

 invisible to the naked eye, there is produced by mechanical means 

 actual light. 3. That the so-called northern light has the strong- 

 est chemical action. 



A further conclusion is, that the light in vacuo of Ruhmkorff's 

 apparatus, or even that of the electric machine, is a much more 

 powerful agent for testing the fluorescence of bodies than any 

 hitherto employed. 



I may here mention that I am still engaged on this subject, 

 and reserve to myself further communications. The short time 

 at my disposal compels me to limit myself to the statement, that 

 a thick white glass in the dark chamber appears of a clear and 

 splendid gray. 



I scarcely doubt that the white colour of the electric light in 

 air has also its explanation in the combination of the higher 

 systems of waves, which are formed in consequence of the mani- 

 fold reflexion on the atoms of air, and the consequent inter- 

 ference. Even the sun's rays are, according to Sondhaus, violet, 

 and we see the sun, as it appears to us, only through a mixture 

 of tints, whose production can be explained by the combination 

 of the shorter systems of rays of the violet light. 



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