THE MASS-LUMINOSITY RELATION 
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According to the present theory a star remains of practically constant 
bolometric magnitude so long as its mass does not alter. More accurately 
the track of evolution of a star of constant mass has a slight upward slope 
to the left; such a track is shown by the dotted line SS'. Any considerable 
vertical displacement in Fig. 4 involves a change of mass. In particular, 
there can be no evolution of a star along QR unless the star is changing