Indeed, a certain fatality seems to have hung over the attempts made in Britain to realize Adams's discovery. In 1845, the Rev. W. R. Dawes, one of the keenest and most skilful of amateur observers, was so much impressed by some of Adams's letters to the Astronomer Royal that he wrote to Lassell, asking him to search for the planet. When Dawes's letter arrived, Lassell was suffering from a sprained ankle, and laid the letter aside till he should be able to resume work. In the meantime the letter was burned by an officious servant-maid, and Lassell lost the opportunity of a discovery which would have crowned the fine work which he accomplished as an amateur observer.
A very different fate had attended Leverrier's calculations. On September 23, 1846, a letter from Leverrier was received at the Berlin Observatory, asking that search should be made for the planet in the position which his inquiries had pointed out. The same night Galle made the search, and within a degree of the spot indicated an object was found with a measurable disc of between two and three seconds diameter. As it was not laid down on Bremiker's star-chart of the region, it was clearly not a star, and by next night its planetary nature was made manifest. The promptitude with which Leverrier's results were acted upon by Encke and Galle is in strong contrast to the sluggishness which characterized the British official astronomers, who, indeed, can scarcely be said to have come out of the business with much credit.
A somewhat undignified controversy ensued. The French astronomers, very naturally, were eager to claim all the laurels for their brilliant countryman, and were indignant when a claim was put in on behalf of a young Englishman whose name had never previously been heard of. Airy, however, displayed more vigour in this petty squabble than in the search for Neptune, and presented such evidence in support of his fellow-countryman's right to recognition that it was impossible to deny him the honour which, but for official slackness, would have fallen to him as the actual as well as the potential discoverer of the new planet. Adams himself took no part in the strife; spoke, indeed, no words on the matter, except to praise the abilities of Leverrier, and gave no sign of the annoyance which most men in like circumstances would have displayed.
Galle suggested that the new planet should be called Janus; but the name of the two-faced god was felt to be rather too pointedly suitable at the moment, and that of Neptune was finally preferred. Neptune is about 32,900 miles in diameter, his distance from the sun is 2,792,000,000 miles, and he occupies 165 years in the circuit of his gigantic orbit. The spectroscopic evidence, such as it is, seems to point to a condition somewhat similar to that of Uranus.
Neptune had only been discovered seventeen days when Lassell found him to be attended by one satellite. First seen on October 10, 1846, it was not till the following July that the existence of this body was verified by Lassell himself and also by Otto Struve and Bond of Harvard. From the fact that it is visible at such an enormous distance, it is evident that this satellite must be of considerable size—probably at least equal to our own moon.
Small instruments can make nothing of Neptune beyond, perhaps, distinguishing the fact that, whatever the tiny disc may be, it is not that of a star. His satellite is an object reserved for the very finest instruments alone.
Should Neptune have any inhabitants, their sky must be somewhat barren of planets. Jupiter's greatest elongation from the sun would be about 10°, and he would be seen under somewhat less favourable conditions than those under which we see Mercury; while the planets between Jupiter and the sun would be perpetually invisible. Saturn and Uranus, however, would be fairly conspicuous, the latter being better seen than from the earth.
Suspicions have been entertained of the existence of another planet beyond Neptune, and photographic searches have been made, but hitherto without success. So far as our present knowledge goes, Neptune is the utmost sentinel of the regular army of the solar system.