Page:Astronomy for Everybody.djvu/256

During the first twenty years of the nineteenth century Bouvard, of Paris, an eminent mathematical astronomer, prepared new tables of the motions of Jupiter, Saturn, and Uranus, then supposed to be the three outermost planets. He took the deviations of these planets, produced by their attraction on each other, from the calculations of Laplace. He succeeded fairly well in fitting his tables to the observed motions of Jupiter and Saturn, but found that all his efforts to make tables that would agree with the observed positions of Uranus were fruitless. If he considered only the observations made since the discovery by Herschel, he could get along; but no agreement could be obtained with those made previously by Flamsteed and Lemonnier, when the planet was supposed to be a fixed star. So he rejected these old observations, fitted his orbit into the modern ones, and published his tables. But it was soon found that the planet began to move away from its calculated position, and astronomers began to wonder what was the matter. It was true that the deviation, measured by a naked eye standard, was very small; in fact, if there had been two planets, one in the real and one in the calculated position, the naked eye could not have distinguished them from a single star. But the telescope would have shown them well separated.

Thus the case stood until 1845. At that time there lived in Paris a young mathematical astronomer, Leverrier, who had already made a name in his science, having