In 1781 Sir William Herschel discovered the planet Uranus, an event that doubled the size of the solar system. After extensive observation, astronomers soon realized that its orbit was inconsistent and, moreover, was being disturbed by the gravitational force of an unknown object. They soon set out to find that object by calculating the amount by which it affected the orbit of Uranus. Using Sir Isaac Newton's Law of Gravity, astronomers had been able to study the gravitational interactions between planets in some detail. Deviations from the predicted motions were easily noticed, and the probable location of the perturbing object could be fairly easily estimated.

In 1841, John Couch Adams, a twenty-two-year-old astronomy and mathematics student, used these principles to conclude that the irregularities of Uranus's orbit were caused by another planet further away from the Sun. He had first assumed that the planet tugging Uranus was in the same...