﻿408 M. A. Wiillner on the Spectra of 



To the reddish-yellow part succeeds, first of all, a feebly illu- 

 minated green field bounded on the right by a brighter green 

 band. Then follows, as far as the line H (3, which always remains 

 visible, a beautiful green multifariously shaded field, which by its 

 shading and the bright bands standing out from the darker back- 

 ground, four of them being particularly bright, makes quite a 

 stereoscopic impression. The character of this part is so like 

 that of the green in the first nitrogen- spectrum, that only a 

 closely detailed comparison makes the difference perceptible. 



From H ft on the blue side,, the spectrum reaches to about the 

 middle of the space between H (3 and H 7 ; and here also against 

 the faint blue ground four brighter bands stand out, of which 

 the second and the fourth are the brightest. H 7 can only be 

 occasionally faintly seen. 



I have since then observed just the same spectrum in a tole- 

 rable number of other hydrogen-spectrum-tubes when, after 

 being for a long time used with a well-working induction-appa- 

 ratus, they were illuminated by a feebler current. 



The observation of MM. Pliicker and Hittorf, that continuous 

 spectra of the first order belong to a lower temperature than the 

 spectra of the second order (consisting of individual bright lines), 

 led to the supposition that this spectrum also belonged to a 

 lower temperature, which might result from the circumstance 

 that, after lengthened use (perhaps through partial melting of 

 the electrodes), the induction-current on entering the gas met 

 with a greater resistance. If this supposition were correct, the 

 method already adopted by Pliicker and Hittorf for producing 

 the second spectra (the simultaneous interposition of a Leyden 

 jar into the current of the induction-apparatus) must also again 

 produce the spectrum of hydrogen consisting of the characteristic 

 lines. This supposition was so far confirmed that, on introdu- 

 cing a Leyden jar, the above-mentioned spectrum-tube exhibited 

 a flickering, alternately red and white light, and that, viewing 

 the flickering up of the red light with the spectrometer, the well- 

 known three lines were observed. 



The change of the continuous spectrum into that consisting 

 of the three lines was effected with the aid of Holtz's machine. 

 If the current of such a machine without a condenser was allowed 

 to pass through the hydrogen-tubes, their light appeared white, 

 and, viewed with the spectrometer, the continuous spectrum ap- 

 peared, though faint, yet distinct, especially in the green. If 

 the condenser was laid upon the machine, so that the spark tra- 

 versed the tube in individual discharges, the light of the tube at 

 once became red and exhibited only the characteristic lines. The 

 same was of course seen when, by means of a Holtz's machine, 

 the discharges of a small Leyden jar with a small striking-dis- 



