252 



SPECTROSCOPE AND VARIOUS SPECTRA [Ch. VIII 



constitution (fig. 148), and their width, in part, upon the thickness 

 of the body. With some colored bodies, no definite bands are present. 

 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. 



Pcrmatv 



Fig. 148 



Spectra to Show Different Kinds of Absorption Bands. 



Solar Spectrum The spectrum of daylight showing the dark, fixed lines 

 (Fraunhofer lines) A B C D E F G, and the wave lengths in microns, .70, .60 

 .50, .40. 



Sodium The spectrum of incandescent sodium. With this spectroscope it 

 is a single bright yellow band (D) at about X0.59/Z, all the rest of the spectrum 

 being dark. 



Perman. potash The spectrum of a solution of permanganate of potash and 

 has five absorption bands, two being especially dark and sharply outlined. 



Methaemoglobin The spectrum of methaemoglobin with several absorption 

 bands, the two in the yellow-green being darkest. The blue end of the spec- 

 trum is also greatly shortened. 



These spectra have the blue end at the right instead of at the left (compare 

 fig. 144, 146-147). 



§ 397. Angstrom and Stoke's law of absorption spectra. — The 

 waves of light absorbed by a body when light is transmitted through 

 some of its substance are precisely the waves radiated from it when 

 it becomes self-luminous. For example, a piece of glass that is 

 yellow when cool gives out blue light when it is hot enough to be 

 self-luminous. Sodium vapor absorbs two bands of yellow ' light 

 (D lines) ; but when light is not sent through it, but itself is luminous 



