CKLEST1AL CHEMISTRY. 255 



being attained, and the facility which will then be afforded of com- 

 parison of the more refrangible and less luminous parts of the stellar 

 spectra, when thus self-registered, with existing metallic charts, must 

 be obvious. 



Careful examinations are also in progress of Lyrae (Vega) ; Ca- 

 pella ; Arcturus ; a Cygni ; Rigel ; a. Andromeda? ; llegiilus ; (i Pe- 

 gasi, and many others, from which most interesting results may be 

 predicated. 



One of the most important and interesting deductions which the 

 observers, Avhose work we have been discussing, draw from tln-ir 

 results, is connected with the origin of the colors of the stars. That 

 there is great variety of tints among these bodies is well known ; 

 white, yellow, and red stars are the most frequent, whilst in double 

 stars the contrasted colors are often green or blue.* The source of 

 the light of the stars, as well as of that of the sun, must be a solid or 

 liquid body in a state of incandescence, as only such bodies, when 

 raised to a high temperature, give a continuous spectrum. In the 

 case both of the sun and stars, this continuous spectrum becomes 

 crossed by dark bands, which are produced by the absorbing power 

 of the constituents held in a vaporous form in the investing atmos- 

 pheres. These atmospheres vary in chemical constitution according 

 to the elements composing the star, and should the dark lines pro- 

 duced by the absorptive power of the vapors forming the stellar atmos- 

 phere, and which correspond to the bright lines they would form in an 

 incandescent state, be the strongest and most numerous in the more 

 refrangible portions of the spectrum, then the star would have a red 

 or orange tint, because this part of the spectrum would suffer least 

 absorption ; while, on the contrary, should the red and yellow por- 

 tions have most lines, the blue and green rays would predominate in 

 the color of the star. The frequency of the lines in the orange, green, 

 and blue of Aldebaran's spectrum, previously pointed out, is strongly 

 in favor of this theory, as the red is left little affected, and the other 

 tints are subdued by the dark lines. Orionis has the red, green, 

 and blue rays much diminished, which produces the orange color of 

 this star; and fi Pegasi, which much resembles a Orionis in its spec- 

 trum, has a deep yellow hue. In Sirius, which is of a brilliant white, 

 there are no lines sufficiently intense in any particular part of the 

 spectrum to interfere Avith our receiving the light in about the same 

 proportion, as to the quantity of the different colored rays, to that 

 which starts from the incandescent light-giving surface. 



It became a matter of great interest to test this theory with respect 

 to the double stars, which present the most marked difference in color ; 

 but the faintness of the blue or green companions rendered the obser- 

 vations very difficult. Still, observations of (9 Cygni and ct Herculis 

 were obtained, which accord remarkably with the theory just pro- 

 pounded. Thus, in the bright star of (9 Cygni, which is light orange 



*Thc examination of these double stars, side by side, in the spectroscope, is a 

 matter of great difficulty, on account of their difference of size and light ; while, 

 from their proximity, the examining instrument is liable to be sufficiently dis- 

 turbed by shakes and accidents as to put one or the other out of the Held of view. 

 The labor, too, is extremely fatiguing to the eye on account of their difference in 



brightness. 



