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ANNUAL OF SCIENTIFIC DISCOVERY. 



matic or solar spectrum. (See figure.) When the solar spectrum is 

 received upon a white screen, it appears at first glance to be a contin- 

 uous band of colored light (red, orange, yellow, green, blue, indigo, 



and violet) ; but by taking certain precautions, the luminous band 

 may be seen in reality to be traversed in the direction of its breadth 

 by numerous dark lines, varying, however, in different parts, in width 

 and distinctness ; these lines are independent of the nature of the re- 

 fracting medium used, and they always occur in the same color and 

 at corresponding parts of the spectrum. The position of some of the 

 most conspicuous lines observed in the solar spectrum was long ago 

 accurately determined by Fraunhofer, who designated them by the 

 letters 5, (7, Z>, E, F, G, and H, as represented in the figure. It 

 has also been long known that the position of these dark lines varies 

 with the source of the light yielding the spectrum ; the spectrum 

 yielded by solar light having one system of lines, and the spectrums 

 from other or artificial lights having other systems or peculiarities. 



It is at this point that the investigations of Messrs. Bunsen and 

 Kirchhoff may be properly said to have commenced. They found 

 that when a metallic or other elementary substance is burned or evap- 

 orated in a gas flame, and the light of the flame is passed through a 

 prism and refracted to form a spectrum, the spectrum so formed has 

 bright lines crossing it, which are peculiar to or characteristic of the 

 metal or element present in a state of vapor in the flame yielding the 

 light ; or, in other words, the light from one metal or element will 

 present lines in one part of its spectrum, and that from another metal 

 lines in a different part ; the light of each metal or element having 

 always its own characteristic lines with invariable uniformity. The 

 German philosophers have also satisfied themselves that the appear- 

 ance of these peculiar lines in the several spectrums may be regarded 

 as absolute proof of the presence in the flames of certain metals, and 

 that they serve as reactions, by means of which these bodies may be 

 recognized with more certainty, greater quickness, and in far smaller 

 quantities than can be done by help of any other known analytical 

 method, no matter what may be the nature of the body with which 

 the metals are combined. 



