44 The Mickoscope. 



Brewster published a map known as Brewster's & Gladstone's, con- 

 taining dark lines by atmospheric influence or absorption in various 

 parts of the spectrum. These telluric or atmospheric lines are most 

 plainly seen when the sun is low on the horizon, because the strata 

 of vapors and moisture which the rays have to traverse, are more com- 

 pact and longer. Sir John Hirshel investigated the spectrum of 

 flames, especially of strontium, in 1827, affirmed, that in this way we 

 could detect extremely small quantities of this body. 



Swan published, in 1855, that the yo o ottfo P^^*^ '^^ ^ grain of 

 chloride of sodium would respond to the spectrum test. 



In 1824 Talbot discovered and described the bright lines of 

 lithium and strontium, and he did not hesitate to say, "that by 

 means of spectrum analysis we can distinguish the minutest quan- 

 tities of these substances." 



Then came the examination of the electric arc by Frauen- 

 hofer, Wollaston, Focoult, Masson, Angstroem, Van der Willigen and 

 Dore. 



Pflucker examined the spectra of various gases in tubes made 

 by Giessler. 



Janson investigated the absorbing powers of steam and water 

 vapor. 



Pater Sechi, of Rome, discovered by means of the spectroscope, 

 water vapors in the vicinity of the sunspots. 



Sir Charles Wheatstone, in 1835, says in his historical report on 

 the prismatic decomposition of electric, voltaic and electro-magnetic 

 sparks: " These differences are so obvious, that one metal can easily be 

 distinguished from the other by the optic appearance of its spark.'' 

 Then came the most interesting investigations of Angstroem, in 1857. 

 He mapped more than 1000 of these sunlines, and this map, unsur- 

 passed in correctness and amplitude, is known as the map of Ang- 

 stroem and Thalen. 



Such was the condition of spectral analysis when Kirchhof and 

 Bunsen, two eminent savans at the University of Heidelberg, with 

 an improved spectroscope of their own construction, initiated their 

 wonderful and brilliant discoveries, which have revolutionized the 

 entire field of solar, stellar and siderial chemistry. One of the ear- 

 liest fruits of their labors, was the discovery of two new alkaline 

 metals hj Bunsen in 1860. He was engaged in the examination of the 

 alkalies left from the evaporation of a quantity of the mineral waters 

 from the springs at Durkheim. On examining them by the spectro- 

 scope, he saw some bright lines which he had never observed before. 



