About the Author Slides from the Lecture Presidential Lecture 1992 - James A. Van Allen

Figure 1. Illustrations of the principle of propelling an object into a durable orbit about the Earth. The diagram on the right is from Isaac Newton's De Mundi Systematic (1731 Edition) and the one on the left is a modern adaptation thereof (G. Abell, Exploration of the Universe, 4th Ed., Saunders College Publishing, New York, 1982).


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