CELESTIAL CHEMISTRY. 237 



measnred lines form but a small part of the numerous fine lines 

 which may be seen in the sjiectra of these stars. 



" Beneath the spectrum of each star are represented the bright 

 lines of the metals which have been compared with it. These 

 terrestrial spectra appeai'ed in the instrument as you now see 

 them upon the screen, in juxtaposition with the spectrum of the 

 star. By such an an-angement, it is possible to determine with 

 great accuracy whether or not any of these bright lines actually 

 coincide with any of the dark ones. For example : — 



" This closely double line is characteristic of sodium. You see 

 that it coincides, line for line, with a dai-k line simihirly double 

 in the star. The vapor of sodium is therefore present in the 

 atmosphere of the star, and sodium forms one of the elements of 

 the matter of this brilliant but remote star. 



"These tliree lines in the green are produced, so fiir as we 

 know, by the luminous vapor of magnesium alone. These lines 

 agi-ee in position exactly, line for line, with three dark stellar 

 lines. The conchision, therefore, appears well founded, that 

 another of the constituents of this star is magnesium. 



"Again, there are two strong lines peculiar to the element 

 hydrogen ; one line has its place in the red part of the spectrum, 

 the other at the blue limit of the green. Both of these corre; 

 spond to dark lines of absorption in the spectrum of the star'. 

 Hydrogen, therefore, is present, in the star, 



" In a similar way, other elements, among them bismuth, anti- 

 mony, tellurium, and mercury, have been shown to exist in the 

 star. 



"Now, in reference to all these elements, the evidence does 

 not rest upon the coincidence of one line, which would be worth 

 but little, but upon the coincidence of a group of two, three, or 

 four lines, occurring in ditferent pails of the spectrum. Other 

 corresponding lines are probably also present, but the faintness 

 of the star's light limited our comparisons to the stronger lines of 

 each element. 



" What elements do the numerous other lines in the star repre- 

 sent? Some of them are jDrobably due to the vapors of other ter- 

 restrial elements, which we have not yet compared with these 

 stars. But may not some of these lines be the signs of primary 

 forms of matter unknown upon the earth ? Elements new to us 

 may here show themselves, which form large and important 

 series of compounds, and therefore give a special character to the 

 physical conditions of these remote systems. In a similar 

 manner the spectra of terrestrial substances have been compared 

 with several otiier stars. Five or six elements have been de- 

 tected in Betelgeux. Ten other elements do not appear to have 

 place in the constitution of this star. 



" P Pegasi contains .... sodium, magnesium, and perhaps barium ; 



Siriiis contains sodium, magnesium, iron, and hydrogen; 



a Li/rcB ( Ffl/a) contains . . sodium, magnesium, iron; 



p Pollux contains .... sodium, magnesium, iron. 



About sixty other stars have been examined, all of which appear 



