SIX LECTURES ON LIGHT. 



LECTURE VI. 



of Spectrum Analysis: Solar Chemistry: 

 Summary and Conclusions. 



We have employed, as our source of light 

 in these lectures, the ends of two rods of coke 

 rendered incandescent by electricity. Coke 

 is particularly suitable for this purpose, be- 

 cause it can bear intense heat without fus on 

 or vaporization. It is also black, which 

 helps the light; for, other circumstances be- 

 ing equal, as Ihown experimentally by Bal- 



four Stewart, the blacker the body the 

 brighter will be its light when incandescent. 

 Still, refractory as carbon is, if we closely ex-' 

 amine our voltaic arc, or stream of light be- 

 tween the carbon-points, we should find there 

 incandescent carbon-vapor. We might also 

 | detach the light of this vapor from the more 

 ! dazzling light of the solid points, and obtain 

 ! its spectrum. This would be not only les.i 

 ' brilliant, but of a totally different character 

 j from the spectra that we have already seen. 

 i Instead of being an unbroken succession t>f 

 ' colors from red to violet, the carbon-vapor 



