384 ASTRONOMY 



actually fewer of these stars in the Milky Way than outside of it. 

 One class of stars, the fifth type, Class O, has a very remarkable 

 spectrum and distribution. A large part of the light is monochromatic. 

 Of the ninety-six stars of this type so far discovered, twenty-one are 

 in the large Magellanic Cloud, one in the Small Magellanic Cloud, and 

 the remainder follow the central line of the Milky Way so closely, 

 that the average distance from it is only two degrees. All of these 

 stars, with the exception of sixteen, have been found by means of the 

 Henry Draper Memorial. 



It will be seen from the above discussion, that stellar photometry 

 in its broadest sense furnishes the means of attacking, and perhaps of 

 solving, the greatest problem presented to the mind of man, the struc- 

 ture and constitution of the stellar universe, of which the solar sys- 

 tem itself is but a minute and insignificant molecule. 



