146 



MR. CHARLES DE WATTEVILLE ON FLAME SPECTRA. 



(2.) The Prism Spectrographs. 



Each of the spectra to be afterwards described has been obtained afresh in the 

 Physical Research Laboratory at the Sorbonne by means of two prism -spectrographs. 

 One of these, intended for the visible portion of the spectrum, is provided with a 



x x Rutherford-Steinheil prism. The other, 

 which answers the requirements of 

 EDER,* is composed of two lenses and 

 an excellent prism of quartz, worked 

 by M. WERLEIN, of Paris, and allows 

 the whole spectrum to be obtained on 

 one plate. I will not describe the 

 adjustment of this apparatus, the details 

 of which will be found very clearly and 

 practically stated in the paper of 



M. HEMSALECH.t 



The arrangements for obtaining the 

 comparison spectra in this case were as 

 follows : The burner B, the central 

 holes of which had been closed up, was 

 fixed upon a support which also carried 

 a bar of insulating material A, along 

 which the electrodes E, E' could slide. 

 There would then be a gap in the 

 centre of the flume which would Ix; 

 occupied by the electrodes, and thus 

 the spark could be obtained in the axis 

 of the flame and exactly at the same 

 height as the tips of the small blue 

 cones. A single lens served to direct 

 the light of the flame or the spark into 

 the spectroscope. The two spectro- 

 scopes were placed one on either side of 

 the burner, as indicated in the figure, 

 and they could thus be used simultaneously. Here, as in the case of the grating 

 photographs, the spark spectrum fell in the centre of the spectrum of the flame, 

 dividing it into two regions, of which the one corresponded to the inner cone, while 

 the other corresponded to the upper portion of the flame. 



Photof/raphic Methods. For the grating photographs 1 have used EDWARDS' 



* 'Wiener Denkschr.,' 57 (1890). 



t ' Sur les Spectres d'Etincelles,' Paris, HERMANN. 



Fig. 5. 



