Career
Starting in 1847, he worked at the United States. Naval Observatory in Washington, District of Columbia. The asteroid 1745 Ferguson, discovered from the same observatory, was later named in his honour. In 1850, he "lost" a star that he had been observing, which Lieutenant Matthew Maury, the superintended of the Observatory, claimed was evidence for a 9th planet (Pluto had not yet been discovered).
In 1878, however, CHF Peters, director of the Hamilton College Observatory in New York, showed that the star had not in fact vanished, and that the previous results had been due to human error.