IN 1928 Jeans published his Astronomy and Cosmogony, which he considered to be in a sense a sequel to his Problems of Cosmogony and Stellar Dynamics of a decade previous. Actually it comprises much that was in the Adams Prize Essay; but it also includes much original work, besides the contents of a long series of papers in the Monthly Notices of the Royal Astronomical Society. Though this book is exciting and interesting from cover to cover, it cannot be regarded as a masterpiece of the quality of the Adams Prize Essay, for reasons stated earlier. Nevertheless, the ideas on stellar structure contained in this book are well worth recapitulating.

He begins with a survey of the facts of observational astronomy, with an account of the distances of the principal types of astronomical objects, and catalogues in turn the properties of binary stars, variable stars, triple and multiple systems, moving clusters of stars, globular clusters, planetary nebulae, irregular nebulae and extra-galactic nebulae. This leads him to ask the fundamental questions:

What, in ultimate fact, are the stars? What causes them to shine, and for how long can they continue thus to shine? Why are binary and multiple stars such frequent objects in the sky, and how have they come into being? What is the significance of the characteristic flattened shape of the galactic system, and why do some of its stars move in clusters, like shoals of fish, while others pursue independent courses? What is the significance of the extra-galactic nebulae, which appear at a first glance to be other universes outside our own galactic universe comparable in size with it, although different in general quality? and behind all looms the fundamental question: What changes are taking place in this complex system of astronomical bodies, how did they start and how will they end?

Many of these questions were answered in the Adams Prize Essay, and Astronomy and Cosmogony does not carry this part of the story much further. But here we shall try to give an account of Jeans's ideas ‘of the object which occurs most frequently of all in nature's astronomical museum, the simple star’.