APPLIED TO THE HEAVENLY BODIES. 199 



recently found that several of the atmospheric lines in this part of the spectrum 

 are protluced by aqueous vapor. It appears to be very probable that aqueous 

 vapor exists in the atmospheres of Jupiter and Saturn. 



Mars. — On one occasion some remarkable groups of lines were seen in the 

 more refrangible part of the spectrum of Mars. These may be connected with 

 the source of the red color which distinguishes this planet. 



Vcmis — Though the spectrum of Venus is brilliant, and the lines of Fraunhofer 

 were well seen, no additional lines affording evidence of an atmosphere about 

 Venus were detected. The absence of lines may be due to the circumstance 

 that the light is probably reflected, not from the planetary surface, but from 

 clouds at some elevation above it. The light which reaches us in this way by 

 reflection from clouds would not have been exposed to the absorbent action of 

 the lower and denser strata of the planet's atmosphere. 



THE FIXED STARS. 



The fixed stars, though immensely more remote and less conspicuous in 

 brightness than the moon and planets, yet, because they are original sources of 

 liglit, furnish us with fuller indications of their nature. 



To each succeeding age the stars have been a beauty and a mystery. Not 

 only children, but the most thoughtful of men, often repeat the sentiment ex- 

 pressed in the well-known lines — ' 



"Twinkle, twinkle, pretty star; 

 How I wonder what you are." 



The telescope was appealed to in vain, for in the largest instruments the stars 

 remain diskless — brilliant points merely. 



The stars have indeed been i-epresented as suns, each upholding a dependent 

 amily of planets. This opinion rested upon a possible analogy alone. It was 

 n)t more than a speculation. We possessed no certain knowledge y/•o??^ obser- 

 vation of the true nature of those remote points of light. This long and earnestly- 

 coveted information is at last furnished by spectrum analysis. We are now able 

 to read in the light of each star some indications of its nature. Since I have 

 not a magician's power to convert this theatre into an observatory, and so 

 exhibit to you the spectra of the stars themselves, I have provided photographs 

 of careful drawings. These photographs Mr. Ladd will exhibit upon the screen 

 by means of the electric lamp. I will take first the spectra of two bright stars 

 which we have examined with great care. 



The upper one represents the spectrum of Aldebaran, and the other that of 

 Betelgeux, the star marked a in the constellation of Orion. 



The positions of all these dark lines, about 80 in each star, were determined 

 by careful and repeated measures. These measured lines form but a small part 

 of the numerous fine lines which may be seen in the spectra 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 appeared 

 in the instrument as you now see them upon the screen, in juxtaposition with 

 the spectrum of the star. By such an arrangement, it is possible to determine 

 Avitli 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 dark line similarly double in the star. The A^apor 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 three lines in the green are produced, so far as we know, by the lumi- 

 nous vapor of magnesium alone. These lines agree in position exactly line for 



