Page:Lectures on Ten British Physicists of the Nineteenth Century.djvu/129

 the limits within which the planet should be sought; he predicted that it would have a visible disc, and sufficient light to make it conspicuous in ordinary telescopes. By this time Adams had completed his new investigation on the assumption of a distance 1/30 less than before; the results agreed still better with observation. In a letter to Airy he communicated the new results, answered his question about the errors of the radius-vector, and intimated that he was thinking of presenting a brief account of his investigation at the coming meeting of the British Association. Airy at this time was again absent on the Continent; the British Association met; Adams came with his paper, but the section of mathematics and physics had adjourned the day before he arrived. Had he been present at the beginning of the meeting he would have heard Sir John Herschel say in his address on resigning the chair to his successor, after referring to the astronomical events of the year, which included a discovery of a new minor planet: "The year has done more. It has given us the probable prospect of the discovery of another planet. We see it as Columbus saw America from the shores of Spain. Its movements have been felt, trembling along the far-reaching line of our analysis, with a certainty hardly inferior to that of ocular demonstration."

In this same month of September Leverrier sent his predictions to Dr. Galle of the Berlin Observatory in a letter received September 23, 1846. Dr. Galle was already provided with a map of the part of the heavens prescribed, and that very evening he found a star of the eighth magnitude which did not exist on the map; observation on the following evening showed that its motion was nearly the same as that of the predicted planet. On October 1st Challis heard of the discovery of the planet at Berlin. He then found that he had actually noted it on August 4 and August 12, the third and fourth nights of his search, so that had the observations been compared as the work proceeded, the planet might have been discovered by him before the middle of August. The discovery of the planet by Dr. Galle, in consequence of Leverrier's prediction, was received with the greatest enthusiasm by astron-