FOR some years the advocates of the earth's rotundity, and of the Newtonian philosophy generally, were accustomed to refer, with an air of pride and triumph, to the supposed discovery of a new planet, to which the name of "Neptune" was given, as an undeniable evidence of the truth of their system or theory. The existence of this luminary was said to have been predicated from calculation only, and for a considerable period before it was seen by the telescope. The argument was, "That the system by which such a discovery was made, must, of necessity, be true." An article which appeared in the "Illustrated London Almanack," for 1847, contained the following words:--
"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."
If such things as criticism, experience, and comparative observation did not exist, the tone of exultation in which the above-named writer indulges might still be shared in by the astronomical student; but let the following summary of facts and extracts be carefully read, and it will be seen that such a tone was premature and unwarranted.
"In the year 1781, Uranus was discovered by Sir William Herschel. . . . Between 1781 and 1820, it was very frequently observed; and it was hoped that at the latter time sufficient data existed to construct accurate tables of its motions. . . . It was found utterly impossible to construct tables which would represent all the observations. . . . Consequently it was evident that the planet was under the influence of some unknown cause. Some persons talked of a resisting medium, others of a great satellite which might accompany Uranus; some even went so far as to suppose that the vast distance Uranus is from the sun caused the law of gravitation to lose some of its force; others thought of the existence of a planet beyond Uranus, whose disturbing force caused the anomalous motions of the planet; but no one did otherwise than follow the bent of his inclination, and did not support his assertion by any positive considerations. Thus was the theory of Uranus surrounded with difficulties, when M. Le Verrier, an eminent French mathematician, undertook to investigate the
irregularities in its motions. . . . 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." 1
The first paper by M. Le Verrier appeared on the 10th of November, 1845, and a second on June 1st, 1846; and "on the 23rd of September, Dr. Galle, at Berlin, discovered a star of the eighth magnitude, which was proved to be the planet," so it was thought; and hence, had it been true, the Newtonian philosophers had good cause to be proud of the theory which had apparently led to such grand results; and, as in the other "great discovery" by the celebrated French mathematician, M. Foucault, of the earth's motion by the vibrations of a pendulum, the peals of triumph rung by mathematicians were for months ringing in the ears of the whole civilised community. The whole of this scientific rejoicing was, however, suddenly arrested by the appearance, two years afterwards, of a paper by M. Babinet, read before the French Academy of Sciences, in which great errors in the calculations of M. Le Verrier were disclosed, as will be seen by the following letter:--
"Paris, September 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 lustre. 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 revolution 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." 1
"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 '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." 2
Thus we have found that "a discovery which was incontestably one of the most signal triumphs ever attained by mathematical science, and which marked an era that must be for ever memorable in the history of physical investigation," and which "some years ago excited universal astonishment," 3 was really worse than no discovery at all; it was a great astronomical blunder. An error of six hundred millions of miles in the planet's distance, of two thirds in its bulk, and of fifty-one years in its periodic time, ought at least to make the advocates of the Newtonian theory less positive, less fanatical and idolatrous--for many of them are as greatly so as the followers
of Juggernauth--and more ready to acknowledge what they ought never to forget--that, at best, their system is but hypothetical, and must sooner or later give place to a practical philosophy, the premises of which are demonstrable, and which is, in all its details, sequent and consistent. Will they never learn to value the important truth, that a clear practical recognition of one single fact in nature is worth all the gew-gaw hypotheses which the unbridled fancies of wonder-loving philosophers have ever been able to fabricate?
330:1 "Illustrated London Almanack" for 1847.
332:1 "Times" Newspaper of Monday, September 18, 1848.
332:2 "Cosmos," by Humboldt, p. 75.
332:3 "How to Observe the Heavens," by Dr. Lardner, p. 173.