This second edition, originally published in 1929, is an extensive survey at the forefront of cosmology and astronomy with particular reference to the physical state of matter, the structure, composition and life-cycle of stars, and the superstructures of nebulae and galaxies. Intended as a rigourously argued scientific treatise, every effort was made by Jeans to render the results of far-reaching advancements in cosmology intelligible to a broad range of readers.