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communicated to the Academy of Sciences some researches which gave Arago a very high opinion of his abilities. Arago called his attention to the case of Uranus and suggested that he should investigate the subject. The idea occurred to Leverrier that the deviations were probably caused by the attraction of an unknown planet outside of Uranus. He proceeded to calculate in what orbit a planet should move to produce them, and laid his result before the Academy of Sciences in the summer of 1846.

It happened that, before Leverrier commenced his work, an English student at the University of Cambridge, Mr. John C. Adams, had the same idea and set about the same work. He got the result even before Leverrier did, and communicated it to the Astronomer Royal. Both computers calculated the present position of the unknown planet, so that, were it possible to distinguish it from a fixed star, it would only have been necessary to search in the region indicated in order to find the planet. Unfortunately, however, Airy was incredulous as to the matter, and did not think the chance of finding the planet sufficient to go through the laborious operation of a search until his attention was attracted by the prediction of Leverrier, and the close agreement between the two computers was remarked.

The problem of finding the planet was now taken up. Very thorough observations were made upon the stars in the region by Professor Challis at the Cambridge Observatory. I must explain that, as it was not easy with the imperfect instruments of that time to distinguish so