396 Intelligence and Miscellaneous Articles. 



tube, I obtained in succession the following spectra : — 1, the ordi- 

 nary air-spectrum ; 2, the fluted spectrum of nitrogen : 3, that of 

 carbonic oxide ; 4, when the rarefaction was at its maximum, the 

 lines of sodium and chlorine. If to this we add that when a mercu- 

 rial pump is employed the mercury-lines may present themselves, 

 just as those of sulphur may when sulphuric acid is used to dry the 

 gas, the result may easily be a multiplicity of spectra which it would 

 be wrong to attribute to one and the same gas. 



As far as I know, I was the first to observe (in 1853) the spec- 

 trum of hydrogen. Using on that occasion a Leyden jar to produce 

 incandescence of that gas, which was at the pressure of the atmo- 

 sphere, I obtained a spectrum consisting of an intense line in C not 

 clearly limited, and two maxima of light in F and G ; the third maxi- 

 mum, in h, was only observed later. Afterwards Phicker found 

 that by operating with rarefied hydrogen a spectrum is obtained 

 with clearly determined lines. It may thus be regarded as a fact 

 long known, that the spectrum-lines of hydrogen spread when the dis- 

 charge becomes disruptive, and that they end, when the tension of the 

 gas is augmented, by forming a continuous spectrum. M. Wiillner's 

 spectrum No. 4, then, is only the ordinary spectrum of hydrogen. 



Pliicker was the first who indicated a second spectrum for hydrogen, 

 principally characterized by a multitude of lines on both sides of D 

 and towards C. This spectrum generally appears simultaneously with 

 the preceding, but is distinguished from it by several important cha- 

 racters. By causing the discharge of a Ruhmkorff coil to pass in a 

 Geissler's tube containing rarefied hydrogen, in a revolving mirror 

 two images of the incandescent gas are obtained, which correspond 

 to the two spectra : one of them appears as an isolated line, indica- 

 ting that the light there is of very short duration ; the other, on the 

 contrary, widens into a zone traversed horizontally by stria? alter- 

 nately bright and dark. It is necessary, in this experiment, to re- 

 gard the Geissler's tube and the axis of rotation of the mirror as 

 placed vertically. The duration of the last image, in one experi- 

 ment, was from 5 to 6 thousandths of a second *. 



This image disappears immediately the discharge is made disrup- 

 tive by the addition of a condenser. This property, as well as the 

 stratification of the light which accompanies it, indicates that we 

 have here a combination of hydrogen, either with itself or a foreign 

 body ; the latter is the most probable. M. Berthelot has published, 

 in the Comptes Bendus, some observations on a spectrum which he 

 obtained by means of a combination of hydrogen and benzole. He 

 submits that this spectrum belongs to acetylene, and that it has not 

 been previously observed. This, however, is not the case ; having 

 repeated M. Berthelot's experiments with some benzole, I ascer- 

 tained that the spectrum obtained is no other than M. Wiillner's 

 hydrogen-spectrum No. 2. Still, if (as M. Berthelot has shown) 



* To determine the duration of an image, I used M. Kcenig's flames. 

 By projecting simultaneously on the revolving mirror the flame agitated by 

 the pipe, we have a scale by means of which we can easily determine the 

 duration of the luminous phenomena when that duration is very short. 



