At Caltech, as at Chicago, he gathered graduate students and colleagues around him, collaborated with Jesse Greenstein and other Caltech astronomers, brought Patterson with him from Chicago, attracted Bruce Murray from MIT, helped initiate the field of infrared astronomy, introduced new types of telescope instrumentation, and greatly bolstered the involvement of Caltech and its Jet Propulsion Laboratory in NASA's early missions of planetary exploration.

Starting in 1949, Harrison Brown went frequently to Jamaica where he first came in contact with the problems of rapid population growth and technological backwardness in the Third World. From this experience he wrote his most famous book, a monumental survey of the human prospect entitled The Challenge of Man's Future, published by the Viking Press in 1954 and reprinted in 1984.

In this book he contended that the division of human society into a set of industrialized, relatively prosperous nations containing a minority of the world's population, and a set of primarily agrarian nations containing an impoverished majority, is not only unsatisfactory from a humane point of view but is fundamentally unstable and cannot persist. Either the agrarian nations would become industrialized, he argued, or the collapse of machine civilization would produce a mainly agrarian world of virtually universal poverty and misery. Whether the first outcome would materialize would depend on mankind's achieving a stable human population size, a sustainable agriculture and industry, harmony with its environment, peace, and freedom.

Bertrand Russell and Albert Einstein proposed in 1955 an international conference of scientists, including scientists of the two great antagonists in the Cold War, the Soviet Union and the United States, to discuss the dangers and the possible control of nuclear weapons and problems of