John Couch Adams - Discovery of Neptune

Discovery of Neptune

In 1821, Alexis Bouvard had published astronomical tables of the orbit of Uranus, making predictions of future positions based on Newton's laws of motion and gravitation. Subsequent observations revealed substantial deviations from the tables, leading Bouvard to hypothesize some perturbing body. Adams learnt of the irregularities while still an undergraduate and became convinced of the "perturbation" theory. Adams believed, in the face of anything that had been attempted before, that he could use the observed data on Uranus, and utilising nothing more than Newton's law of gravitation, deduce the mass, position and orbit of the perturbing body. On the 3rd of July 1841, he noted his intention to work on the problem.

After his final examinations in 1843, Adams was elected fellow of his college and spent the summer vacation in Cornwall calculating the first of six iterations. While he worked on the problem back in Cambridge, he tutored undergraduates, sending money home to educate his brothers, and even taught Mrs. Ireland, his bedmaker, to read.

Supposedly, Adams communicated his work to James Challis, director of the Cambridge Observatory, in mid-September 1845 but there is some controversy as to how. On 21 October 1845, Adams, returning from a Cornwall vacation, without appointment, twice called on Astronomer Royal George Biddell Airy in Greenwich. Failing to find him at home, Adams reputedly left a manuscript of his solution, again without the detailed calculations. Airy responded with a letter to Adams asking for some clarification. It appears that Adams did not regard the question as "trivial", as is often alleged, but he failed to complete a response. Various theories have been discussed as to Adams's failure to reply, such as his general nervousness, procrastination and disorganisation.

Meanwhile, Urbain Le Verrier, on 10 November 1845, presented to the Académie des sciences in Paris a memoir on Uranus, showing that the pre-existing theory failed to account for its motion. On reading Le Verrier's memoir, Airy was struck by the coincidence and initiated a desperate race for English priority in discovery of the planet. The search was begun by a laborious method on 29 July. Only after the discovery of Neptune on 23 September 1846 had been announced in Paris did it become apparent that Neptune had been observed on 8 and 12 August but because Challis lacked an up-to-date star-map it was not recognized as a planet.

A keen controversy arose in France and England as to the merits of the two astronomers. As the facts became known, there was wide recognition that the two astronomers had independently solved the problem of Uranus, and each was ascribed equal importance. However, there have been subsequent assertions that "The Brits Stole Neptune" and that Adams's British contemporaries retrospectively ascribed him more credit than he was due. But it is also notable (and not included in some of the foregoing discussion references) that Adams himself publicly acknowledged Le Verrier's priority and credit (not forgetting to mention the role of Galle) in the paper that he gave 'On the Perturbations of Uranus' to the Royal Astronomical Society in November 1846:-

I mention these dates merely to show that my results were arrived at independently, and previously to the publication of those of M. Le Verrier, and not with the intention of interfering with his just claims to the honours of the discovery ; for there is no doubt that his researches were first published to the world, and led to the actual discovery of the planet by Dr. Galle, so that the facts stated above cannot detract, in the slightest degree, from the credit due to M. Le Verrier.

— J C Adams (1846)

Adams held no bitterness towards Challis or Airy and acknowledged his own failure to convince the astronomical world:

I could not expect however that practical astronomers, who were already fully occupied with important labours, would feel as much confidence in the results of my investigations, as I myself did.