Close as Neptune is to us in kinship and distance, as astronomical distances go, we never knew of his existence until sixty-six years ago. He is to us almost a recent arrival in the solar domain, but we know that he has been here as long as we have; and whether he was detached before we were from the great nebula which gave birth to us all, or at about the same time, we know that for long ages before there were eyes on the earth to see him he was, as he still is, circling slowly and majestically around our common center of control. The discovery of Neptune in 1846 created truly a sensation in astronomical circles. And, unlike most sensational happenings, it fully justified the extreme interest it aroused. The computation that led to it was a mathematical triumph, and the final result was a most splendidly convincing proof of the theory of gravitation. For the place of this hitherto unknown planet was found by means of computations based on the fact that at certain times Uranus went a little out of his way, thus showing some disturbing body outside of his orbit pulling him slightly from the course he would otherwise take. The deviation was not much--only about one and three-fourths of a minute, which is equal to about one-seventeenth of the apparent diameter of the moon, or one-sixth of the distance between Mizar and Alcor, situated at the bend of the handle of the Big Dipper, two stars that it is difficult for some eyes to separate.[7] But this slight irregularity of Uranus was enough to set at least two able men at work in an effort to locate the disturbing cause. These two men were Adams, of England, and Leverrier, of France. [7] See, in _The Friendly Stars_, “The Seven Stars of the Dipper.” The result of Adams’s work was announced to the Astronomer Royal in England in the autumn of 1845; but the actual search for the planet in the place predicted was delayed until the following summer. In the mean time Leverrier had completed his work and had communicated with astronomers in Berlin, directing them where to look for the planet. The facilities for that sort of work were then better in Berlin than in England; and within half an hour after the search was begun, on the night of September 23, 1846, the new planet was discovered a little more than half a degree from the exact position Leverrier had found for it. It was first recognized as having a sensible disc, and within a day its motion was apparent. No wonder the astronomical world was thrilled by this achievement!