﻿406 M. A. Wiilmer on the Spectra of 



refracting angle with great dispersive power, and through a tele- 

 scope of about twelvefold magnifying-power, this field is resolved 

 into about from fourteen to sixteen bright dark-edged and beau- 

 tifully shaded bands, which are red, orange, yellow to yellowish 

 green. With different hydrogen-tubes this part is seen of differ- 

 ent degrees of brightness, so that Pliicker originally ascribed it to 

 the last traces of air still present in the tubes. 



Pliicker subsequently recognized that this part of the spectrum 

 also belonged to hydrogen. In an investigation made with M. 

 Hittorf on the spectra of ignited gases and vapours*, they 

 show that several elements, as nitrogen and sulphur, have two 

 different spectra — a continuous one with shaded bands, and one 

 consisting of bright lines separated more or less by dark spaces ; 

 these are designated by them as spectra of the first and of the 

 second order. In this investigation they describe this bright field 

 as a special spectrum of hydrogen of a peculiar character. Pliicker 

 says there, in reference to this spectrum : — " In an old spectrum- 

 tube which contained very rarefied hydrogen, the ground against 

 which the three characteristic lines stand out is not always of the 

 same degreeof darkness; sometimes new and brilliant lines appear, 

 especially near the sodium-line. We confirmed the existence of 

 a new hydrogen spectrum, which corresponds to a lower tempe- 

 rature, but exhibits no similarity to all the other spectra of the first 

 order, those of nitrogen, sulphur, &c. In this spectrum, of a pe- 

 culiar character, we observed, when it was fully developed, a great 

 number of well-defined lines, almost too numerous to be counted 

 or drawn, but bright enough to be investigated with a magni- 

 fying-power of 72." 



That this spectrum is peculiar to hydrogen was further con- 

 firmed by passing the discharge of a RuhrnkorfPs apparatus 

 through a tube ^ to \ inch wide, which contained hydrogen 

 under a pressure of 5 to 10 millims. ; a bluish-while line was 

 then observed in its axis. Analyzed with the prism, it exhibited 

 the spectrum in question, especially numerous bright lines be- 

 tween red and yellow. Along with these lines neither H u nor 

 H7 appeared, only H/3,but feebler than many other lines. When a 

 Leyden jar with an increasing charge was interposed, all the lines 

 were brighter, H ft most so, H a appeared beautifully, H 7 more 

 feebly. 



2. About two years ago I observed a third additional spectrum 

 of hydrogen, which neither in its appearance nor in its formation 

 agreed with those already described; for especially in its green 

 part the spectrum has decidedly the character of one of the first 

 order, and at first I considered it belonged to nitrogen, from 

 which, however, more accurate comparison showed that it differed 

 * Pliicker and Hittorf, Philosophical Transactions, 1865, part 1. 



