86 



to that which existed in the case of sun-spots 

 before high dispersion had been applied to the 

 analysis of their light. Many stellar lines which 

 appear single under low dispersion are actually 

 'blends" of several lines, and small displacements 

 due to pressure and other physical phenomena in 

 stellar atmospheres are beyond the reach of exist- 

 ing instruments. As already stated, a beginning 

 has been made in attacking such problems with the 

 6o-mch reflector, but the greater light-collecting 

 power of the loo-inch telescope is required for the 

 continuation of this investigation. 



In view of certain statements in the public press, 

 it may be remarked here that faint stars photo- 

 graphed for the first time with large telescopes are 

 not regarded by astronomers as discoveries, just 

 as the first detection of a new sun-spot is not 

 considered in this light. But the value of a large 

 telescope does come in part from its power of 

 bringing such faint stars within the range of inves- 

 tigation, as their study may add largely to our 

 knowledge of the universe. 



1 he advantages of great light-gathering power 

 were appreciated by the late Mr. John D. Hooker, 

 of Los Angeles, who in 1906 gave to the Mount 

 Wilson Observatory a sum of money to provide a 

 telescope mirror of 100 inches aperture. Many 

 difficulties have been experienced in obtaining a 

 suitable disk of glass, on account of the great 

 thickness (13 inches) required to prevent bending. 

 A disk weighing 4! tons, made by the St. Gobain 



