Urbain-Jean-Joseph Leverrier

Some days ago we heard how Ceres was found by Father Piazzi. Today we shall hear how a Catholic discovered the planet Neptune.

A name known even to those who are not specialists in science is that of the great master of the theory of the planets, Urbain Jean Joseph Leverrier (born 1811 at Saint-Lô, died 1877 at Paris, where he was Director of the Observatory). Who indeed could fail to have heard of the discovery of Neptune, the existence and the location of which Leverrier demonstrated mathematically, and which was thereupon actually discovered by Galle of Berlin in the place indicated? The achievement compelled the admiration of all Europe. "It was a discovery", said Piazzi Smith on the death of Leverrier, "which almost took men's breath away for the moment in astonishment and admiration: and showed that the age of intellectual giants cast in the mould of Newton and Laplace was not yet closed." The name of Leverrier was in every mouth, and honours and distinctions were showered on him from every quarter.

And yet the discovery of Neptune is not perhaps Leverrier's greatest service to Astronomy. Even without his famous computation, Neptune must have been before long discovered. But what science might not yet have attained, were it not for Leverrier's mathematical genius, his masterly grasp of every intricacy of celestial mechanics, and his iron industry and perseverance, is the exact determination of the theory of the planetary system as a whole. For it was this that Leverrier chose as the main business of his life.

The great Astronomer had begun his career in 1836 with some theses in chemistry. But three years later we find him busy with astronomical calculations, a field which he was not to abandon till death. In 1839 he published a mathematical calculation of the variations of the planets during the period 100,000 B. C. to 100,000 A. D., in which he perfected Laplace's imperfect proof that despite the disturbing influence of the planets on one another, the planetary system can never of its own intrinsic forces fall into disorder. In 1843 he worked out the path of Mercury: in 1845 Arago, then Director of the Observatory, recommended him to study the path of Uranus, the most distant of the planets at that time known. By November of this latter year he had worked out a full computation of the path of that planet on the assumption that no influence was operative save that of the planets already known. In June 1846 there followed an essay in which the path thus computed was compared with actual observations, and it was shown that in order to explain the divergences from the path it was necessary to posit the existence of another planet lying outside Uranus. On August 31 1846 Leverrier published a computation of the path of this new body, the existence of which he had thus deductively established. Subsequent observations proved that he was not deceived, and led to the most remarkable of all the discoveries of Astronomy.

In the years 1844-1847 there appeared exhaustive studies of certain of the comets which revolve about the sun, those, namely, which are called after Lexell, Faye, and De Vico. Leverrier traced up the history of these comets, showed by colossal calculations how their paths must have been, and must in the future be, determined by the influence of the planets, especially of Jupiter, and sought to ascertain when these comets became associated with the solar system, and when they will once again pass out of the sphere of influence of the sun.

The planet tables then employed were not in complete agreement with actual observations; the divergences were slight, but still large enough to indicate some mistake in the assumptions on which they were founded. On July 2 1849 Leverrier laid before the Academy the "gigantic plan" of a new computation of these tables. "This Herculean labour", as Tisserand calls it, "he continued down to his death, and he had the fortune and glory to bring it by his sole efforts to a consummation." Mercury, Venus, the Earth, and Mars occupied twenty years: the other planets which presented still greater difficulties were computed in a shorter space.

Amongst the honours bestowed on Leverrier for these brilliant achievements were the dignity of Senator of the Empire, and the Directorate of the Paris Observatory (1854). It may be doubted, however, whether Leverrier was precisely the man for this latter position. He worked, throughout the night "and grudged even a few hours rest to his body, exhausted by continuous labours of this kind. The result was a severe and tedious illness, which had an unfavourable influence on his character" Thus his subordinates found him a hard taskmaker, and the exacting demands he made on them were not mitigated by any courtesy or consideration of manner. Under his Directorate the Observatory exhibited great activity, the results of which are to be found in its publications, but the discontent with Leverrier became so acute that in the year 1870 the Government removed him from his position. Three years later he was, however, restored, for Leverrier was one of those men who cannot be dispensed with. Nor was it his staff alone that had experience of the great savant's ability to make himself unpleasant. When under the Third Republic orders were issued that the motto "Liberté, Fraternité, Egalité" should be inscribed on all public buildings, and even on churches, Leverrier refused to allow any other inscription over the door of the Observatory except the single word Observatoire, and the Government had to give him his ways.

Leverrier was known in France as a "Clerical". "Under the Empire", complained a Paris newspaper, on his reappointment, "he was a clericalising senator, pledged no less deeply to the interests of the altar than to those of the throne." In a discourse pronounced at his funeral, Tresca declared that the study of the heavens had only confirmed and deepened his lively faith in Christianity. It was given to him, said Dumas on the same occasion, to write the last word of the last page of his immortal work in the last hour of his life, murmuring as he concluded: Nunc dimittis servum tuum, Domine. ["Now O Lord you can dismiss your servant" Lk2:29] On June 5 1876 Leverrier laid before the Academy the last instalment of his great work, containing the tables of Jupiter and Saturn. Referring to the speech in which J. B. Dumas had a few days before declared against materialism, he said:

"Throughout this protracted undertaking, lasting over thirty years, we have had need to draw support from the spectacle of one of the glories of creation, and from the ~ thought that our study tended to confirm us in the imperishable truths of the spiritualistic philosophy. It was then with profound emotion that I heard at the last meeting of the Academy, our illustrious permanent Secretary re-affirm those great principles which are the very source of the purest science. That declaration will remain as an honour and an inspiration to French science: and I esteem it a great happiness to have this opportunity of rising in the midst of our Academy, and proclaiming my cordial adhesion to his principles."

[Kneller, Christianity and the Leaders of Modern Science]

I should point out that this Dumas mentioned was a great chemist and also a Catholic; he was a teacher of Pasteur. (We may see him in a future posting.)

There's more to tell, and it is a bit detailed, but connects Leverrier with another great physicist, and is perhaps even more thrilling than the discovery of Neptune:

Leverrier in 1845 found that the advance per century of the perihelion of Mercury was twice as great as the value accepted in Newton's time and that of the total value of 574 seconds of arc, 42 seconds could not be accounted for by any conceivable pattern of perturbation. Inspired no doubt by his discovery of Neptune, Leverrier in 1859 assigned the unaccountable 42 seconds of arc to the effect of a hypothetical planet having the same mass as Mercury but being at half the distance of Mercury from the Sun. In the same year an amateur astronomer, Lescarbault, claimed to have observed the transit of a small round object across the sun's disc. Some of Lescarbault's observations were promptly accepted by Leverrier, who named the new planet Vulcan and computed its revolution around the sun as twenty days. Despite the fanfare, the most competent astronomers, Leverrier included, were unable to observe Vulcan. Leverrier, however, had already cast his lot with Vulcan. When, on April 4, 1876, Weber announced at Peckeloh that he had seen Vulcan's transit, Leverrier's confidence was bolstered again, and he fixed the transits of Vulcan for March 22, 1877, and October 15, 1882. On the appointed days nothing was sighted with any certainty. Such was also the case during the total solar eclipse of July 15, 1878. Meanwhile, the true amount of the advance of the perihelion of Mercury was subjected to further observations, and Newcomb in 1884 put the amount unaccountable by any known or conceivable factor at 43 seconds of arc per century. To clear up this puny but stubborn discrepancy between theory and observation, an even more drastic step than finding a new planet was needed to do full justice to a mere 43 seconds of arc that takes a full hundred years to accumulate. ...

When the first consistent solution came, the most universal and most respected of all physical laws, Newton's account of the motion in a central field of force, was viewed in a much different light: it was only the particular case of a law of much wider sweep, the General Theory of Relativity. Nowhere else, perhaps, had the edge of precision influenced so forcefully the course science was to follow. The satisfactory account for 43 seconds of arc per century was actually the first experimental evidence Einstein could claim for his theory. To see his equations so complicated (if judged by the standards of ordinary calculus) yield the exact amount, was for Einstein, as he wrote in his letter of November 28, 1915, to Sommerfeld, one of the most exciting times of his life. "The marvelous thing which I experienced was the fact that not only did Newton's theory result as first approximation but also the perihelion motion of Mercury (43" per century) as second approximation."
[Jaki, The Relevance of Physics 244-5, quoting Schilpp (ed.), Albert Einstein: Philosopher-Scientist]

Wow.

I hope you caught Jaki's clever pun: "viewed in a much different light".

Also see here for more about Leverrier.