The Discovery of Neptune

Uranus was the first new planet to be discovered observationally (in 1781 by Sir William Herschel, see Georgium Sidus). Scientists quickly used Newton's Laws to calculated Uranus' expected orbit. When that orbit was actually measured, though, it was found to be slightly off. In 1824 Friedrich Wilhelm Bessel suggested that another planet, beyond Uranus, could account for the deviation.

English mathematician John Couch Adams set himself the task of calculating the expected characteristics and position of this mystery-planet in 1843. He found a solution in 1845, but in spite of the rigorous refinement of his calculations, Adams was ignored by the Royal Astronomer at Greenwich.

Meanwhile in France, French mathematician Urbain Leverrier decided to try his hand at the same problem. In 1846 he was able to independently duplicate Adams' results. Leverrier was more persistent than Adams, though. After he too was ignored by his national observatory, Leverrier sent his results to Johann Galle at the Berlin Observatory who quickly found the planet Neptune.

The discovery of Neptune based on a mathematical prediction was seen as evidence for the universality of Newton's Laws of Gravitation.