72 THE SUN. 



also by differences in the material of which they con- 

 sisted. 



(31.) Every observer who has examined the spectrum 

 with more care than the last, has added to the number 

 of these lines. Dr Wollaston first noticed two or three 

 of the most "conspicuous. Fraunhofer registered and 

 fixed the places of some thirty or forty more ; and later 

 observers have mapped down with all the precision of a 

 geographical survey, not less than two thousand of them. 

 The knowledge of them, and the precise measurement of 

 their distances from one another, has proved most valu- 

 able in a great many lines of scientific enquiry, and most 

 particularly in Optics and Chemistry and, quite recently, 

 has been the means of revealing facts respecting the con- 

 stitution of the sun itself, which one would have supposed 

 it impossible for man ever to have become acquainted 

 with. One word more on these lines for we must hus- 

 band time, as there remains a great deal more ground 

 to go over. I have said that they are not occasional, but 

 belong to the sun's light as such. But they may be con- 

 sidered as in some sort accidental as regards the sun for 

 the light of each of the stars when thrown into a spec- 

 trum, is found to have a different system of these " fixed 

 lines." And what is more, the light of every flame has 

 its peculiar lines, which indicate the nature of the burn- 

 ing substance. And in this way there seems to arise a 

 possibility that by studying these lines carefully, as ex 

 hibited by terrestrial flames and other sources of artificial 

 light, we may come to a knowlege of what the sun and 

 stars are made of. This is what men of science are now 



