“These remarkable calculations have pointed out a position which has very nearly proved to be the true one.
“On September 23, Dr. Galle at Berlin discovered a star of the eighth magnitude, which has proved to be the planet. Its place at the time was five degrees from Delta Capricorni. It was found to have a disc of 3 seconds as predicted; and its longitude at the time differs less than a degree from the longitude computed from the above elements. Its daily motion, too, is found to agree very closely with the predicted; and, judging from this last circumstance, the planet’s distance, as stated above, must be nearly the truth.
“Thus the result of these calculations was the discovery of a new planet in the place assigned to it by theory, whose mass, distance, position in the heavens, and orbit it describes round the Sun, were all approximately determined before the planet had ever been seen; and all agrees with observations, so far as can at present be determined. It is found to have a disc, and its diameter cannot be much less than 40,000 miles, and may be more; its motions are very slow; it is at present in the constellation of Aquarius as indicated by theory; and it will be in the constellation of Capricornus all the year 1847. It may be readily seen in a telescope of moderate power.
“Whatever view we take of this noble discovery it is most gratifying, whether at the addition of another planet to our list; whether at the proving the correctness of the theory of universal gravitation; or in what view soever, it must be considered as a splendid discovery, and the merit is chiefly due to theoretical astronomy. This discovery is perhaps the greatest triumph of astronomical science that has ever been recorded.”[33]
[33] “Illustrated London Almanack for 1847.”
If such things as criticism, experience, and comparative observation did not exist, the tone of exultation in which the above article indulges might be properly shared in by the astronomical student; but let the following extracts be carefully read, and it will be seen that such a tone was premature and unwarranted. “Paris, Sept. 15, 1848. The only sittings of the Academy of late in which there was anything worth recording, and even this was not of a practical character, were those of the 29th ult. and the 11th inst. On the former day M. Babinet made a communication respecting the planet Neptune, which has been generally called M. Le Verrier’s planet, the discovery of it having, as it was said, been made by him from theoretical deductions, which astonished and delighted the scientific public. What M. Le Verrier had inferred from the action on other planets of some body which ought to exist was verified, at least so it was thought at the time, by actual vision. Neptune was actually seen by other astronomers, and the honour of the theorist obtained additional luster. But it appears from a communication of M. Babinet that this is not the planet of M. Le Verrier. He had placed his planet at a distance from the Sun equal to thirty-six times the limit of the terrestrial orbit; Neptune revolves at a distance equal to thirty times of these limits, which makes a difference of nearly two hundred millions of leagues! M. Le Verrier had assigned to his planet a body equal to thirty-eight times that of the earth; Neptune has only one third of this volume! M. Le Verrier had stated the revolutions of his planet round the Sun to take place in two hundred and seventeen years; Neptune performs its revolutions in one hundred and sixty-six years! Thus then Neptune is not M. Le Verrier’s planet; and all his theory as regards that planet falls to the ground! M. Le Verrier may find another planet, but it will not answer the calculations which he had made for Neptune. In the sitting of the 14th, M. Le Verrier noticed the communication of M. Babinet, and to a great extent admitted his own error! He complained indeed that much of what he said was taken in too absolute a sense; but he evinces much more candour than might have been expected from a disappointed explorer. M. Le Verrier may console himself with the reflection that if he has not been so successful as he thought he had been, others might have been equally unsuccessful, and as he has still before him an immense field for the exercise of observation and calculation, we may hope that he will soon make some discovery which will remove the vexation of his present disappointment.”[34]
[34] “Times” Newspaper, Monday, Sept. 18, 1848.
“As the data of Le Verrier and Adams stand at present there is a discrepancy between the predicted and the true distance; and in some other elements of the planet. It remains, therefore, for these or future astronomers to reconcile theory with fact; or, perhaps, as in the case of Uranus, to make the new planet the means of leading to yet greater discoveries. It would appear, from the most recent observations, that the mass of Neptune, instead of being as at first stated one nine thousand three hundredth is only one twenty three thousandth that of the Sun; whilst its periodic time is now given with a greater probability at 166 years; and its mean distance from the Sun nearly thirty. Le Verrier gave the mean distance from the Sun thirty-six times that of the Earth; and the period of revolution 217 years.[35]
[35] “Cosmos,” by Humboldt, p. 75.
“May 14, 1847. A Paper was read before the Royal Astronomical Society, by Professor Schumacher, ‘on the identity of the planet Neptune (M. Le Verrier’s) with a star observed by M. Lalande in May, 1795.’”[36]