Masterpieces of Science 



be horizontal dark spaces or gaps in our spec- 

 trum. Or again, if we failed in finding gaps of 

 this sort by simply narrowing the aperture, we 

 might lengthen the spectrum by increasing the 

 refracting angle of the prism, or by using several 

 prisms and so on. 



The first great discovery in solar physics, by 

 means of the analysis of the prism (though the 

 discovery had little meaning at the time), con- 

 sisted in the recognition of the fact that by 

 means of such devices as above, dark gaps or 

 cross-lines can be seen in the solar spectrum. In 

 other words, light-waves of the various grada- 

 tions corresponding to all the tints of the spec- 

 trum from violet to red, do not travel to us from 

 the great central luminary of our system. Re- 

 membering that the effect we call colour is due 

 to the length of the light-waves, the effect of red 

 corresponding to light-waves of the greatest 

 length, while the effect of violet corresponds to 

 the shortest light-wave, we see that in effect the 

 sun sends forth to the worlds which circle around 

 him light -waves of many different lengths, but 

 not of all lengths. Of so complex and interesting 

 a nature is ordinary daylight. 



But spectroscopists sought to interpret these 

 dark lines in the solar spectrum, and it was in 

 carrying out this inquiry which even to them- 

 selves seemed almost hopeless, and to many 

 would appear an utter waste of time that they 

 lighted upon the noblest method of research yet 

 revealed to man 



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