The son of a wealthy merchant, Halley was attracted to astronomy after seeing two comets as a child. By the age of eighteen he had found errors in authoritative tables on the positions of Jupiter and Saturn and by nineteen had published a paper on the laws of Johannes Kepler. In 1676 Halley left England for St. Helena, an island west of Africa, to map the southern constellations, a task never before undertaken. Although the climate of St. Helena proved less than ideal for Halley's purposes, he was able to catalogue 341 stars before returning to England. His pioneering work on the island assured his place in England's scientific community and Halley was awarded a master's degree from Oxford as well as election to the Royal Society.

In 1684 Halley entered into a conversation with biologist Robert Hooke and architect Christopher Wren (1632-1723) that concerned the force that drove the movement...