386 THE CHEMISTRY OF THE SUN. [CHAP. 



like a spindle or a half-spindle, with the bulging portion in some 

 cases on the more, in others on the less, refrangible side. It 

 is very difficult to understand what process is here at work 

 if we are not in presence of separations brought about by 

 temperature. 



The flame phenomena also give us an opportunity of observ- 

 ing the inverse appearance of spectral lines. The following is 

 a case in point: In one photograph of the flame given by 

 manganese the line at wave-length 4234'5 occurs without the 

 triplet near wave-length 4030, while in other photographs the 

 triplet is present without the line at 4234'5. 



The following photographs taken before 1879, 1 may be referred 

 to as showing some details of the phenomena now under 

 discussion. 



Photographs showing the spectrum of core and flame of arc compared. 



Barium, showing that of two lines (wave-length 4130'5 and 4282 '5) of equal 

 intensity in the core, the less refrangible was visible almost alone in the flame. 



Strontium, showing two lines at 4078*5 and 4215'3. In the core the more 

 refrangible has a much broader reversal than the other, while in the flame the less 

 refrangible exists alone and reversed. 



Manganese, in the flame-spectrum of one of these photographs the triplet at 

 about 4030 '0 exists with no other manganese lines ; while it is absent from the 

 flame-spectrum of the other photograph, although the manganese line at 4234 '8 is 

 present. 



Photographs showing reversal of phenomena by reversing the current. 



Two spectra of lead, obtained by normal current and reversed current, showing 

 that the lines which, in the upper spectrum were thickened at their lower 

 extremities, were in the lower spectrum thickened at their upper extremities, 

 and that the general appearance of the two sets of lines was reversed. 



Two spectra of copper showing the same phenomena. 



Photographs showing the lines en echelon in the spectrum. 



Spectrum of manganese obtained with the large arc of a Siemens' machine, in 

 which the want of symmetry is so conspicuous that if a straight line be drawn 

 through the centre of the photograph it will cut one set of lines at their centres, 

 another near their upper extremities, while a third set of lines will be cut near 

 their lower extremities. 



' . 1 Proc. Roy. Soc. vol. xxviii. p. 427. 



