CH. VI] MICRO-SPECTROSCOPE AND POLARISCOPE 



159 



spectrum (Fig. 136). If now the spirit-lamp flame, colored by the incan- 

 descent sodium, is placed in the path of the electric light, and it is examined 

 as before, there will be a continuous spectrum, except for dark lines in place 

 of the bright sodium lines. That is, the comparatively cool yellow light of 

 the spirit lamp cuts off or absorbs the intensely hot yellow light of the electric 

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

 scope 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 incan- 

 descent metal vapors (sodium, iron, etc.), but that they are so cool in com- 

 parison with the rays of their wave length in the sun that the cooler light of 

 the incandescent metallic vapors absorb the light of corresponding wave 

 length, and are, like the spirit lamp-flame, unable to make up the loss, and 

 therefore the presence of the dark lines. 



I 215. Absorption Spectra from Colored Substances. — While the solar 

 spectrum is an absorption spectrum, the term is more commonly 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 spec- 

 tra of colored objects which are not self-luminous, i. e., blood and other 

 liquids, various minerals, as monazite, etc. The spectra obtained by examin- 

 ing 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 less sharply defined. Their number and position depend on 

 the substance or its constitution (Fig. 137), and their width, in part, upon the 

 thickness of the body. With some colored bodies, no definite bands are pres- 

 ent. The spectrum is simply restricted at one or both ends and various of the 

 other colors are considerably lessened in intensity. This is true of many 

 colored fruits. 



So so 



Fig. 137. Absorption spectrum of Oxy-hemoglobin or arterial blood (1) 

 and of Hemoglobin or venous blood (2). {From Gamgee and McMunn.) 



A, B, C, D, E, F, G, H. Some of the. Principal Fraunhofer lines of the 

 solar spectrum (\ 192). 



.go, .80, .70, .60, .50, .40. Wave lengths in microns, as shown in Ang- 

 strom's scale (? 224). It will be seen that the wave lengths increase toward the 

 red and decrease toward the violet end of the spectrum. 



Red., Yellow, Orange, etc. Color regions of the spectrum. Indigo should 

 come between the blue and the violet to complete the seven colors usually given. 

 It was omitted through inadvertence. 



