Scientist of the Day - John Couch Adams

Portrait of John Couch Adams, mezzotint by Samuel Cousins after a drawing by Thomas Mogford, 1851, National Portrait Gallery, London (npg.org.uk)

John Couch Adams, an English astronomer, was born June 5, 1819.  Until the 21st century, in the oft-told story of the discovery of the planet Neptune, Adams had played the role of the star-crossed hero (a doubly appropriate designation for an observer of the skies). As the tale used to be related, the existence of Neptune was independently predicted in 1845-46 by two individuals: Adams, and a French astronomer, Urbain Le Verrier, both basing their predictions on perturbations (slight orbital irregularities) in the position of the 7th planet, Uranus. Both predictions supposedly had Neptune in the same relative position in the sky. Adams petitioned George Airy, the Astronomer Royal, to search at the predicted location, and Airy turned the task over to James Challis at Cambridge in the summer of 1846, and Challis failed to find a new planet. Meanwhile, Le Verrier, who was unable to find local support in Paris, asked an astronomer in Berlin, Johann Galle, to look for it, and Galle spotted it, just where Le Verrier had said it would be in a published paper, on the very first night of his search, Sep. 26, 1846. Had Challis searched properly, or had Airy shown more than lukewarm support for Adams, the 8th planet would have been an English prize, and not ill-gotten French booty, in the British version of the tale. Airy himself lamented his hesitancy in public and claimed that Adams had made the same prediction as Le Verrier and should be credited with the co-discovery of Neptune. And so he has always been – until 25 years ago.

Opening paragraph of paper, “An explanation of the observed Irregularities in the Motion of Uranus…, read by John Couch Adams, Nov. 13, 1846, Monthly Notices of the Royal Astronomical Society, vol. 7, p. 149, 1846 (Linda Hall Library)

A problem facing historians who wanted to reexamine the story of the discovery of Neptune was that the "Neptune file," the record at Greenwich Observatory of the events and documents involving Adams, Challis, and Airy, had long ago gone missing. But in 1999, it turned up, in – of all places – Chile, stolen and taken there by a miscreant astronomer. The file revealed that Adams had not given just one prediction in 1845 for the position of a new planet – he had given quite a few of them, each one in a different location, making it virtually impossible for anyone to look for it. When Neptune was discovered by Galle, Airy apparently went back through Adams' predictions and picked out the one that was closest to the mark, hid away all the others, and made that prediction public, supporting his claim that Adams should be credited with co-discovery, and blaming himself for not following up. In a sense, Airy sacrificed himself on the altar of British astronomy, ensuring that England and Adams would prevail, even if Airy did not. I borrowed this last sentence from our post on Airy, where you can learn more about this interesting but devious man.

Disclaimer of John Couch Adams at being a co-discoverer of Neptune, in his paper, “An explanation of the observed Irregularities in the Motion of Uranus…, Monthly Notices of the Royal Astronomical Society, vol. 7, p. 150, 1846 (Linda Hall Library)

So Adams was not a co-discoverer of Neptune after all.  Adams should be credited with considerable mathematical skill in making any kind of a prediction of the existence of an 8th planet based on the perturbations of a 7th – in fact, only Adams and Le Verrier, of all the world’s astronomers – thought it was possible to do such calculations. But Le Verrier made only one prediction, which was borne out by observation, and Adams made quite a number of different predictions, none of which led to the discovery of a new planet.

It should be noted and stressed that Adams himself never claimed any credit as a co-discoverer of Neptune. The Royal Astronomical Society, at its meeting of Nov. 13, 1846, after Neptune had been observed by Challis, read into the record all sorts of letters between Airy, Challis, Adams, and Le Verrier, which were subsequently printed in the Monthly Notices of the Society, and at that meeting Adams read a paper of his own, offering a brief account of his involvement in the problem for the past three years (second image). After showing that his calculations preceded those of Le Verrier, he went on to say:

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

It should be further noted that while I have referred to the newly discovered 8th planet as Neptune, for ease of discussion, it did not acquire that name until later.  Le Verrier, in fact, wanted to name the planet after himself.  You can read more about the naming problem in our post on Le Verrier.

Title Page, International Conference held at Washington for the Purpose of Fixing a Prime Meridian and a Universal Day. Protocols of the Proceedings, 1884 (Linda Hall Library)

Adams went on to a very successful career at Cambridge, where he was director of the Observatory.  Late in his life, he participated in a conference that perhaps was more helpful to British astronomy than any prediction about a new planet. In 1884, Adams attended the International Meridian Conference in Washington, D.C, as one of the British delegates at this international gathering, and he went home with the Prime Meridian, making Greenwich Observatory the internationally agreed-upon location for the zero-degree longitude line (fourth image). Since the French desired the prime meridian badly for either Paris or the Canary Islands, that was a not inconsiderable achievement, and we might offer this as Adams’ great legacy, rather than the discovery of Neptune.

Portrait of John Couch Adams, oil on canvas, by Hubert von Herkomer, 1888, National Portrait Gallery, London (npg.org.uk)

There are two portraits of Adams in the National Portrait Gallery in London: one showing him in 1851, just after the events surrounding Neptune (first image), and the other, painted in 1888, depicting the older astronomer who had recently brought home the Prime Meridian (fifth image).

William B. Ashworth, Jr., Consultant for the History of Science, Linda Hall Library and Associate Professor emeritus, Department of History, University of Missouri-Kansas City. Comments or corrections are welcome; please direct to ashworthw@umkc.edu.