The Development of Our Ideas about Our Galaxy and Other Stellar Systems up to 1925
A General Survey of Galaxies, Their Forms and Composition
The Recognition of Two Types of Stellar Populations
The Stellar Population II
Dust and Gas as the Basic Features of the Spiral Structure in Galaxies
Spiral Arms as the Birthplace of Stars of the Population I
Spiral Structure and Star Formation in Our Own Galaxy
Foerster Lectures on the Immortality of the Soul
Charles M. and Martha Hitchcock Lectures
Howison Lectures in Philosophy
Jefferson Memorial Lectures
Bernard Moses Memorial Lecture
Carl O. Sauer Memorial Lecture
Barbara Weinstock Lectures on the Morals of Trade
