MECHAIN (PETER FRANCIS ANDREW), a well known practical astronomer and geographer, was born at Laon, 16th April 1744.
His father was an architect, and educated him with the intention of making him his successor in his business. He was afterwards obliged to take charge of two young men at Sens, as their private tutor; and he accidentally became acquainted with Lalande on occasion of the sale of a fine instrument which he had procured, and of which Lalande became the purchaser; and it was under Lalande's patronage that he was brought forward as an observer, surveyor, and computer. He made two voyages with Mr de la Bretonniere, and assisted him in surveying some parts of the coast of France. He was afterwards employed in various computations by the Marquis de Chabert and the Duc d'Ayen.
Having obtained a prize from the Academy of Sciences in 1782, for a Memoir on comets, he became a member of the Academy the same year. Having proved that the hopes entertained by some astronomers of recovering an old comet were unfounded, he made up in some measure for the disappointment, by finding them eleven new ones in the course of eighteen years; and he computed the orbits not only of all these, but of thirteen others, which had been discovered by other observers: emulating in this department the labours of both his predecessors, Messier and Pingré.
About 1785, he undertook the publication of the Connaissance des Temps, and continued it till he was employed in geodetical operations at a distance from Paris. He was appointed, together with Cassini, de Thury, and Legendre, to make a committee to meet the English astronomers for the determination of the relative situation of the observatories, which had been proposed by Cassini. It was in these operations that he first brought Borda's circle into general use. He was soon after, in 1789, made a Foreign Member of the Royal Society of London.
In 1791, he was appointed, in conjunction with Delambre, to execute the intentions of the Constituent Assembly, with regard to the determination of a basis of linear measures. A variety of delays and difficulties occurred in these operations; in Spain he was wounded in the head and in the side, by an ac-
Méchain. incident which occurred while he was inspecting a water-wheel; and the political circumstances of the times produced many embarrassments, which caused him to linger in Italy perhaps a little longer than was actually necessary; but the establishment of the Bureau des Longitudes, and his nomination as a member of it, determined his immediate return to Paris. He was now director of the Observatory, and he entered with great zeal on a series of observations, which were to rival those of Flamsteed, of Bradley, or of Maskelyne; but he seems to have been a little tired of the confinement, and he readily accepted, or rather solicited, the appointment to take a part in the measurements required for the still further extension of the arc of the meridian to the south of Barcelona. But the secret motive for his seeking this humbler employment appears to have been a desire to remove some doubts which he entertained respecting the latitude of Barcelona, as it appeared after his death from his papers, that there had been a discordance of 3" in some observations which he had not made public. In this unfortunate undertaking, he paid a heavy penalty for any want of candour which may have been attributed to the concealment; shipwreck and disease awaited him; and he died at last, at his post, the 20th September 1805, of a fever, which fatigue and a bad climate had brought on. The severe stage of his illness was so short, that his son, who accompanied and assisted him in the survey, had not time to join him.
From the time of his accident in Spain he had become habitually melancholy and timid, though regardless of personal danger in the pursuit of his professional objects. His whole time was occupied in observing and calculating: he published little; and never hazarded to advance any reflections on the subjects which employed him, being probably more in the habit of acting than of speculating. He married, in 1777, Miss Thérèse Marjon, with whom he had become acquainted at Versailles. This connexion was in every respect happy; he was indebted to it for a competent fortune, and he left a daughter and two sons.
1. Of his publications we find the most important in the Mémoires des Savans Étrangers; that is, besides some Observations of eclipses and occultations, a Mémoire on the comets of 1582 and 1661; showing that they are not the same; and their non-appearance seven or eight years afterwards fully justified his conclusions, and the adjudication of the prize.
2. In the Mémoires of the Academy, from 1782 to 1784, there are several of his Observations of transits, eclipses, occultations, and comets.
3. There are also some letters of Méchain in Zach's Geographical ephemerides about 1800, on the instruments of the Parisian Observatory, and on other subjects.
4. He edited the Connaissance des temps, from 1786 to 1794. See LALANDE.
5. Base du système métrique, décimal. 3 v. 4. Paris, 1806, 1807, 1810. The joint work of Méchain and his respectable and indefatigable friend and colleague Delambre.
[Delambre, Mém. Instit. Sc. VI. 1806, p. i.; and Merionethshire. in Biographie Universelle, XXVIII. 8. Paris, 1821.] (M. E.)