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If a beam of light, admitted through a small vertical slit about one-six- 

 teenth of an inch wide, be caused to fall upon the first prism in the series, it 

 will be bent in its passage through that prism, and its rays will be separated 

 also in consequence of the different lengths of the various waves compos- 

 ing the beam. As these fall upon the second prism they will be still more 

 refracted or bent and still more widely dispersed. 



These effects will be increased by each prism of the series through 

 which the beam is successively passed, and in this manner the lines in the 

 spectrum may be spread out with great distinctness for careful investiga- 

 tion. In this way the colors are of course ranged horizontally and not 

 one above the other. 



By the arrangement of several prisms as described, the lines have been 

 more accurately studied. Some of these bands are composed of sev- 

 eral smaller bands, while others are composed of innumerable dark 

 threads. The amount of labor expended in carefully mapping out these 

 lines, locating them accurately upon charts and measuring their relative 

 distances from each other, and in various other scientific observations of 

 them, is really wonderful. Among these laborers, besides Fraunhofer, 

 are to be named Kirchhoff, Bunsen, Angstrom, Janssen, Lockyer, and seve- 

 ral others. 



These dark interruptions in the solar spectrum were rightly believed to 

 be caused by rays from the sun, which from some cause failed to reach 

 the earth with an intensity equal to that of the brilliant ones revealed by 

 the vividco ors of the spectrum. 



To Kirchhoff belongs the glory of having solved the enigma of these 

 missing rays, and in their solution Science has received a power of ana- 

 lyzing both terrestrial and celestial matter, surpassing in delicacy of test 

 and exceeding in amplitude of research all that the wildest dream of 

 the imagination could have suggested. 



It seems incredible that the ingenuity of man should have enabled him 

 to perfect an instrument by which he can detect with absolute certainty, 

 in the slightest dust brushed from his clothes, a trace of metal so m'nute 

 that one hundred and eighty millions of such particles would weigh but a 

 single grain; and with the self-same instrument analyze with equal cer- 

 tainty the chemical constituents of worlds so infinitely remote in the re- 

 gions of stellar space, that the human mind utterly fails even to conceive 

 distances so profound. 



I will endeavor to explain some of the wonderful revelations of this 

 marvelous instrument, for which we are mainly indebted to Kirchoff. 



The spectrum of the electric light exactly resembles that of the sun 

 except that Frauenhofer's lines are absent from it. Incandescent metals 

 produce continuous spectra like the electric lamp, but the vapors of such 

 metals do not create continuous spectra. They simply produce one or 

 more independent bright lines. 



By so arranging a prism that a beam of sunlight was passed through 

 its upper end, and a beam from an electric lamp through its lower end,. 

 Kirchhoff produced the two spectra upon the same screen, the one immedi- 



