Page:Lectures on Ten British Physicists of the Nineteenth Century.djvu/128

 cipal result was that the mean longitude of the planet for 1st of October, 1845, was 323° 34′. Adams was hurt at the reception which his results had obtained; regarding Airy's question as of trifling importance he did not send any answer immediately but applied himself to a new calculation on the assumption of a smaller mean distance.

That same November a French astronomer, M. Leverrier, presented a paper to the French Academy on the perturbations of Uranus produced by Jupiter and Saturn, and concluded that these were quite incapable of explaining the observed irregularities. In June of the next year he presented his second paper which showed that there was no other possible explanation of the discordance, except that of an exterior planet. Further, like Adams, he assumed the distance to be double that of Uranus, and calculated that its longitude at the beginning of the next year (1847) would be 325°. Leverrier communicated his results by letter on the 24th of June to Airy, who on comparison found that there was only about one degree of difference in the predicted places of Adams and Leverrier. The next day (June 29) a meeting of the Board of Visitors took place at the Greenwich Observatory; Sir John Herschel and Prof. Challis were present as visitors. In the course of a discussion, Airy referred to the probability of shortly discovering a new planet, giving as his reason the close coincidence of Adams' and Leverrier's predictions. Early in July Airy thought it time that a search should be made for the planet. He considered the Cambridge telescope the best for the purpose, and he asked Prof. Challis whether he would undertake it, and the latter agreed to do so. Airy suggested the formation of three successive maps of the stars down to the 4th magnitude, in a band of the heavens 30° long by 10° wide having the predicted place of the planet as its centre. When the successive sets of observations were mapped, the planet could be detected by its motion in the interval.

At the end of August Leverrier presented his third memoir to the French Academy in which he gave the calculated elements of the orbit of the planet. He also restricted as far as possible