10 



SECTION PHYSICS. 



of the stars, even on the supposition that the stars do not really differ 

 greatly as to the substances which compose them. 



The spectroscope has revealed to us the true nature of the nebulce. 

 This diagram represents the latest results of a comparison of the lines 

 of the nebula with terrestrial spectra. 



Of the four bright lines, the two more refrangible ones appear cer- 

 tainly to show the presence of hydrogen. The brightest line appears 

 In a small instrument to be coincident with the brightest line in the 

 spectrum of nitrogen. A more critical examination shows the nebular 

 line to be single, while the nitrogen line is double. The line of the 

 nebula is sensibly coincident with the less refrangible of the components 

 of the double line of nitrogen. 



Spectrum of the Nebula in Orion. 



Nebula 



Hydrogen 

 Nitrogen 



Hy H/3 N 



The same method of research has told us, that, a part at least of the 

 light of comets is emitted by the cometary matter in a state of gas. 

 Further, that this matter contains carbon in some form, probably 

 combined with hydrogen. 



Spectrum of 

 WinnecMs 

 Comet, 1868 



Carbon Spark 



taken in 

 Olefiant Gas. 



When the presence of a terrestrial substance has been established in 

 a star, then it is possible by a more critical comparison with greater 

 dispersive power to find out whether the star is in motion relatively to 

 the earth in the line of sight. 



If a small shift in the stellar lines is seen towards the more refrangible 



