256 SCIENCE PROGRESS. 



In that way it very soon became perfectly clear to those 

 who were working at the sun, that in all these disturbances, 

 or at all events in most of them, we were dealing to a large 

 extent with lines not seen in our laboratories when dealing 

 with terrestrial substances ; this work went on till ultimately, 

 thanks to the labours of Professor Young in America, we 

 had a considerable list of lines coming from known and un- 

 known substances which had been observed under these 

 conditions in solar disturbances, and Professor Young was 

 enabled to indicate the relative number of times these lines 

 were visible. For instance, the lines which are most 

 frequently seen under these conditions he tabulated as 

 represented by the number 100, and of course the line 

 which was least frequently seen would be represented by 

 1 ; and therefore from these so-called "frequencies" we 

 got a good idea of the number of times we might expect 

 to see any of these disturbance-lines when anything was 

 going on in the sun. 



It was this kind of work which made Tennyson write 

 those very beautiful lines : 



" Science reaches forth her arms 

 To feel from world to world ". 1 



1 And then he added : 



" and charms 

 Her secret from the latest moon ". 



I mention this because Tennyson, whose mind was saturated with 

 astronomy, had already grasped the fact that what had already been done 

 was a small matter compared with what the spectroscope could do ; and 

 now the prophecy is already fulfilled, for by means of the spectroscopic 

 examination of the light from the stars we can tell that some of them are 

 double stars, that is to say, in poetic language, stars with attendant moons. 

 Although we can thus charm the secret from each moon by means of the 

 spectroscope, to see the moon it would require (in the case of (3 Aurigse) a 

 telescope not eighty feet long, but with an object-glass eighty feet in dia- 

 meter, because the closer two stars are together the greater must be the 

 diameter of the object-glass, independently cf its focal-length and magnifying 

 power. 



