Ch. VIII] SPECTROSCOPE AND VARIOUS SPECTRA 251 



at various levels, sometimes apparently between the colors and some- 

 times in the midst of a color. These are the so-called Fraunhofer 

 lines. Some of the principal ones have been lettered with Roman 

 capitals, A, B, C, D, E, F, G, H, commencing at the red end. The 

 meaning of these lines was for a long time unknown, but it is now 

 known that they correspond with the bright lines of a line spectrum. 

 For example, if sodium is put in the flame of a spirit or Bunsen lamp 

 it will vaporize and become luminous. If this light is examined there 

 will be seen one or two bright yellow bands corresponding in position 

 with D of the solar spectrum (fig. 146, 148). If now the spirit-lamp 

 flame, colored by the incandescent sodium, is placed in the path of 

 the electric light, and it is examined as before, there will be a continu- 

 ous spectrum, except for dark lines in place of the bright sodium 

 lines. That is, the comparatively cool yellow light of the spirit- 

 lamps cuts off or absorbs the intensely hot yellow light of the electric 

 light; and although the spirit flame sends a yellow light to the spec- 

 troscope it is so faint in comparison with the electric light that the 

 sodium lines appear dark. It is believed that in the sun's atmosphere 

 there are incandescent metal vapors (sodium, iron, etc.), but that they 

 are so cool in comparison with the rays of their wave length in the 

 sun that the cooler light of the incandescent metallic vapors absorbs 

 the light of corresponding wave length, and is, like the spirit-lamp 

 flame, unable to make up the loss, and therefore the dark lines are 

 present. 



§ 396. Absorption spectra from colored substances. — While 

 the solar spectrum is an absorption spectrum, the term is more com- 

 monly applied to the spectra obtained with light which has passed 

 through or has been reflected from colored objects which are not 

 self-luminous. 



It is the special purpose of the micro-spectroscope to investigate 

 the spectra of colored objects which are not self-luminous, i.e., blood 

 and other liquids, various minerals, as monazite, etc. The spectra 

 obtained by examining the light reflected from these colored bodies 

 or transmitted through them possess, like the solar spectrum, dark 

 lines'or bands, but the bands are usually much wider and le-s sharply 

 defined. Their number and position depend on the substance or its 



