136 IN STARRY REALMS. 



bow. Thus we demonstrate the highly composite charac- 

 ter of a sunbeam ; but the light from the nebula in Orion, 

 with which we are at present concerned, is of a much 

 more simple character. 



When a beam of the nebular light is transmitted 

 through the prisms, it declares at once that the object 

 from which that light has come is totally different from a 

 star like the sun. Instead of the beautifully coloured 

 band, decked in all the glowing hues of the rainbow, 

 the nebular beam is seen to be composed simply of six 

 or seven widely separated strips. It is important to test 

 the character of the light in these strips. Fortunately 

 this can be done in a way that is completely satis- 

 factory. We can produce artificial lights from known 

 sources, and observe them through the spectroscope simul- 

 taneously with the light of the nebula. 



There are in the composition of this globe some sixty 

 or seventy different elementary substances, and under 

 suitable conditions each one of these substances can afford a 

 perfectly characteristic spectrum. Thus the way of making 

 the comparison with the nebula is to try the different ele- 

 ments one after another, until one can be discovered which 

 pours forth a light that behaves under the prism aa 

 does the light from the nebula. Pursuing this inquiry, 

 Sir W. Huggins found that when hydrogen gas was ignited 

 to incandescence by the passage of electricity, it emitted 

 light which, after passage through the prisms, came to- 

 coincidence with one of the lines in the spectrum of 

 nebula ; and the hydrogen character of two of the other 

 lines has been since demonstrated. It was thus established 

 that hydrogen is one of the constituents of the Great 



