634 



POPULAR SCIENTIFIC LECTURES. 



FIG. 4. 



meat. Apart trom tho proof of two well- 

 . known terrestrial elements, this discovery 

 vas of the utmost importance, since it fur- 

 nished the first unmistakable proof that the 

 cosmical nobuke aro not, for the most part, 

 small heaps of fine stars, but that the greater 

 part of the light which they emit is really due 

 to gaseous bodies. 



The gaseous spectra present a different ap- 

 pearance when the gas is in front of an 

 ignited solid whose temperature is far higher 

 than that of the gas. The observer sees 

 then a continuous spectrum of a solid, but 

 traversed by tine dark lines, which are just 

 visible in the places in which the gas alone, 

 seen in front of a dark background, would 

 show bright lines. Tho solar spectrum is of 

 this kind, and also that of a great number of 

 fixed stars. The dark lines of the solar spec- 

 trum, originally discovered by Wollaston, 

 were first investigated and measured by 

 Fraunhofer, and are hen."e known as Fraun- 

 hofer's lines. 



Tar more powerful apparatus was after- 

 ward nsed by Kirchhoff, and then by 

 Angstrom, to push tho decomposition of 

 light as far as possible. Fig. 4 represents an 



apparatus willi four prisms, constructed by 

 Kteinheil for Kirchhotf. At the further end 

 of the telescope B is a screen with a fine slit, 

 representing a fine slice of light, which can 

 be narrowed or widened by tho small screw, 

 and by which tho light under investigation 

 can be allowed to enter. It then passes 

 through the telescope B, afterward through 

 the four prisms, and finally through the tele- 

 scope A, from which it reaches the eye of the 

 observer. Figs. 5, (5, and 7 represent .smell 

 portions of the solar spectrum as mapped by 

 Kirchhoff, taken from the green, yellow, and 

 golden-yelloM r , in which the chemical symbols 

 below Fe (iron), Ca (calcium \ Na (sodium \ 

 Pb (lead) and the affixed lines, indicate 

 the positions in which the vapors of these 

 metals when made incandescent, either in 

 the flames or in the electrical spark, would 

 show bright lines. The numbers above their, 

 show how far these fractions of Kirchhoffa 

 map of the whole system are apart from each 

 other. Here, also, we see a predominance 

 of iron lines. In the whole spectrum Kirch - 

 boff found not less than 450. 



It follows from this, that the- solar atmos- 

 phere contains an abundance of the vapon 



Fto. 5. 



Put. . 



