SrECTEUM ANALYSIS. 289 



fore, a strong current of electricity is used, excited by a 

 powerful galvanic battery, and the material heated in the 

 electric arc is converted into incandescent vapor, and thus 

 yields a spectrum. Maps have been made showing the 

 thousands of lines which are seen in the spectra of nearly 

 all the elements. The apparatus is difficult to manage and 

 very expensive, so for ordinary work the chemist depends 

 upon the Bunsen burner or alcohol lamp, and confines his 

 research to the lighter metals. 



405. Celestial Spectroscopy. "We have not previously re- 

 ferred to certain peculiarities in the sun's spectrum, be- 

 cause we did not want to tell you too many things at once. 

 If you examine the sun's spectrum with a good spectro- 

 scope having a narrow slit, you will see fine black lines 

 crossing the spectrum. These were observed many years 

 ago by Fraunhofer, a German optician, but no attempt was 

 made to explain them until after the perfection of the 

 spectroscope by Kirchhoff. For good and sufficient rea- 

 sons, which we can not explain to you in this book, it is be- 

 lieved that those black lines give us indications of the ele- 

 mentary bodies burning in the sun. A careful study of 

 these lines by many eminent men has led to a remarkably 

 accurate knowledge of the constitution of the sun. Thus, 

 wonderful as it may appear, we have good reason for be- 

 lieving that the sun contains sodium, calcium, magnesium, 

 iron, copper, zinc, hydrogen, and many other metals; and 

 that the sun does not contain gold, silver, mercury, po- 

 tassium, lead, arsenic, or platinum. More perfect instru- 

 ments may eventually remove some element from this last 

 list and place it among the bodies known to exist in the 

 sun. Not only have astronomers, thus aided by the chem- 

 ist, examined the light of the sun, but they have studied 

 the fixed stars, the nebula?, and comets, thus developing a 

 special branch of spectrum analysis called celestial spectro- 



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