CHAPTER XXVII 

 THE SPECTROSCOPE AND THE STUFF OF COSMOS 



IF we look back upon the gradual advance of human know- 

 ledge, we might almost be led to conceive physical investiga- 

 tion as a kind of game of Hare and Hounds. The hand of 

 nature, as it were, scatters the bits of paper which have en- 

 abled her followers to pursue her track. But sometimes the 

 scent has been so thinly sown, the gaps so far between, 

 that baffled man might have felt as though nature had not very 

 fairly played the game. Perhaps it has added a certain zest ; 

 it has certainly demanded a sharpness of observation, a patience, 

 and a genius of intuition, compared with which the interesting 

 problems of Mr. Sherlock Holmes seem elementary. 



Certainly no puzzle was ever set the mind of man to solve 

 seemingly more elusive than the lines which cross the coloured 

 band formed when a thin beam of sunlight is turned through 

 a prism. As the band is spread wider and wider, the number 

 of these dark lines runs up into thousands ; they seem dis- 

 tributed in no regular order, they appear and disappear under 

 different physical conditions, in seeming hopeless confusion. 



Surely no phenomenon was ever better named than when 

 Newton spoke of this prismatic band as a spectrum a spectral 

 apparition. Could Newton have been told that out from all 

 this tangle we should one day learn the constitution of the 

 sun, of the stars as well their temperature, their motions, 

 their physical states, even that dreamer of wonderful dreams 

 would have sagely shaken his head. How has all this mar- 

 vellous accession of knowledge come ? 



In Newton's time men had settled down to think of light 

 as a substance, that it was due to the emission of infini- 

 tesimal particles, which bombard the eye with incredible speed. 

 Newton's contemporary, Huyghens, had a different idea, that 

 light was not material at all, but, like sound, a form of wave 



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