380 THE CHEMISTRY OF THE SUN. [CHAP. 



great complexity both with regard to colour and concentric 

 envelopes, and we can watch the reversals in the flame as well. 



The spectrum of this flame I have photographed side by side 

 with that of the arc itself; and when the poles are clean the 

 flame has been shown by eye observation to be in part due to 

 the combination of the carbon vapour of the poles with the 

 nitrogen of the air, thus giving us absolute demonstration of 

 combinations brought about among vapours by reduction of 

 temperature : there is also a new spectrum. 



The lines which reverse themselves most readily in the arc are 

 generally those, the absorption of which is most developed in the 

 flame ; thus the manganese triplet in the violet is magnificently 

 reversed in the flame, and the blue calcium line is often seen 

 widened, H and K being not only not absorbed, but entirely 

 invisible. 



In support of the various statements made in chapter xvi., 

 and as illustrating especially the location of the various ab- 

 sorptions, I may refer to the following photographs 1 in my 

 possession : 



Photographs showing passage from truncation to parallelism. 



Spectrum of strontium, showing two reversed lines (wave-lengths 4078 - 5 and 

 4215 '3) gradually broadening towards one end. 



Spectrum of calcium, showing reversal of the blue line, and of H and K. 

 While the blue line presents the appearance of a cone, through the centre of 

 which, the absorption line is bounded by parallel sides, the H and K lines are 

 almost normal in their appearance, showing, however, a slight widening at 

 the pole. 



Spectrum of manganese, showing the blue calcium line tapering to a point at 

 one extremity and enlarging spindle-shaped towards the other end ; the reversal 

 of this line does not extend through its whole length, but merely through the 

 bulging portion, tapering gradually to a point. 



Spectrum of strontium, showing the two lines (4078'5 and 4215*3) which this 

 time present an appearance very similar to the blue calcium line in the last 

 photograph. In the more refrangible line, however, the reversal retaining its 

 tapering form extends through the whole length of the line. 



Spectrum of calcium, in which not only the blue line but also the H and K 

 lines present the appearance of truncated cones. 



1 Exhibited to the Royal Society in 1879. Proc. Rvy. Soc. vol. xxviii. p. 431 



