nous only through reflected light. The stars are so distant from us that any planets which may attend them are beyond the reach of the most powerful telescopes. In some of the planetary and spiral nebulæ, such as the Great Nebula in Andromeda (Fig. 1), we perhaps
observe the earlier stages of the process of condensation, but no distinct evidence of progressive change has yet been gathered from telescopic observation. In seeking for evidence of stellar evolution, on a plan comprehensive enough to include a place for every star in the heavens.