8. Kapteyn believes that he is able to divide the individual
stars--those whose proper motions are known--into the two star
streams which he has described; and he finds that the first
stream is rich in the early blue stars, less rich relatively in
yellow stars, and poor in red stars, whereas the second stream
is very poor in early blue stars, rich in yellows, and
relatively very rich in reds. His interpretation is that the
stream-one stars are effectively younger than the stream-two
stars, on the whole. Stream one still abounds in youthful
stars: they grow older and the yellow and red stars will then
predominate. Stream two abounds in stars which were once young,
but are now middle-aged and old.
