LEMONNIER, Peter (Claude) Charles, a diligent and accurate astronomer, born at Paris, on the 23d of November 1715, was the son of Peter Lemonnier, of St Sever, in Normandy.

His father was a professor of philosophy in the College d’Harcourt, and member of the Academy of Sciences. He distinguished himself, as a teacher, by his activity in promoting the introduction of mathematical reasoning into the Cartesian philosophy. Under such auspices, the son might have enjoyed facilities for the cultivation of any of the sciences; but he soon showed a decided preference for astronomy, and began to be a practical observer before he was sixteen. In the month of November 1732, Mr Fouchy procured him the use of a mural quadrant of three feet radius, and he soon applied himself with diligence to the determination of the sun’s greatest equation, an investigation which he continued for many years; and in 1741, he found the equation to amount to 1° 55' 3ľ'; a quantity differing only by 7" from Delambre’s latest determination.

He presented to the Academy of Sciences, in 1735, an elaborate map of the moon, accompanied by some remarks; and in the month of April of the following year, before he was twenty-one years old, he was made a member of the Academy, in the character of Adjunct Geometrician. He continued to be a constant contributor to its Memoirs for more than fifty years. The winter of 1736 and 1737 he passed at Torneo, with Clairaut and Maupertuis, as a member of a committee appointed by the Academy for measuring a degree in Lapland; and he was not less zealous than any of his colleagues in the execution of that arduous undertaking.

He is considered as having effected, in conjunction with Lacaille, a complete reformation in the practical astronomy of France. He entered very early into correspondence with the English astronomers of the day; they had carried their instruments and modes of observation to a higher degree of perfection than their neighbours; and Lemonnier was of great use to the science, in making known to his countrymen the practical methods of Flamsteed, and in introducing the instruments of Graham and Bird.' In April 1739, he was made a foreign member of the Royal Society of London, and for the last twelve or fourteen years of his life he is said to have been the senior member of the society. He was the first that introduced the effects of nutation, then lately discovered by Bradley, into the solar tables; and he complained bitterly of Lacaille’s injustice, in not giving him due credit for the improvement.

The Due de Noailles made him known to the king of France, who was fond of his company, and showed him many kindnesses. In 1742, he gave him apartments at the Capucins in the Rue St Honoré, where he continued to live till the Revolution. On another occasion, when he had taken great pains to fix an accurate meridian at St Sulpice, the king made him a present of 15,000 livres, which he expended in the purchase of instruments, as the greatest luxury that be was capable of enjoying.

The places of the stars, which he determined in 1740, served Lalande for the purpose of computing their proper motions, though they differed a little from the results of Bradley’s observations. About 1746, he was much engaged in examining the inequalities of Saturn, produced by the attraction of Jupiter; and Euler employed his computations in the theory which obtained a prize in 1748; each confirming the accuracy of the other. He continued to observe the moon, without intermission, for fifty years, though a small part only of his observations was published.

In the year 1748 he went to England, partly for the purpose of obtaining further information from a personal acquaintance with the astronomers and opticians resident in London, and partly in order to observe the solar eclipse [7:13:227] of that year, in a situation where it would be very nearly annular. He proceeded accordingly to Scotland with the Earl of Morton, accompanied by Short the optician, and they observed the eclipse together at Aberdour, an ancient residence of Lord Morton’s, in Fifeshire. They obtained their time from the College at Edinburgh, where there was a transit instrument, by means of the flash of a cannon fired from the castle at twelve, and another five minutes after. “The eclipse was so nearly annular, that, at the nearest approach, the cusps seemed to want about one-seventh of the moon’s circumference to be joined; yet a brown light was plainly observed, both by Lord Morton and myself,” says Mr Short, “to proceed or stretch along the circumference of the moon, from each of the cusps, about one third of the whole distance of the cusps from each cusp; and there remained about one third of the whole distance of the cusps not enlightened by this brown light, so that we were for some time in suspense whether or not we were to have the eclipse annular with us. During the greatest darkness, the planet Venus was seen at Edinburgh, and other places, by a great number of people, but I did not hear of any other stars being seen. The darkness was not great, but th© sky appeared of a faint languid colour.” In fact, our mornings and evenings are always illuminated by a light, which has acquired more or less of a red tinge in its oblique passage through the atmosphere; and when we have a similar light without the redness, the contrast between the sensation and the memory makes it appear “faint,” that is, greenish or grey, instead of white. Mr Lemonnier was particularly anxious to measure the moon’s diameter, which “he found 29'47∣", ’ ' agreeing precisely with the computed diameter, and not requiring any correction for the supposed effects of irradiation. A similar remark was made by a very accurate practical astronomer in the eclipse of 1820.

In order to verify the position of his mural quadrant, which was of eight feet radius, and made by Bird, Lemonnier felt the advantage of having a moveable one to compare with it, and he procured a block of marble eight feet by six, and fifteen inches thick, turning on an axis, to which he fixed his smaller instrument, of five feet radius, in order to be able to reverse its position. He devoted a considerable portion of his time to the investigation of the laws of magnetism, and especially to the variation of the compass; and he endeavoured to ascertain the effect of the moon’s influence on the winds, and on the atmosphere in general.

Lemonnier had long disputed the accuracy of the Parisian base, measured by Cassini and Maraldi, but he was at last convinced that his objections were groundless. He was originally a most zealous friend and patron of Lalande; but afterwards, having taken offence at some slight cause, he refused to see him for many years. In fact, he appears to have been somewhat obstinate and irritable; but he is said to have had genius, zeal, activity, and intelligence, as well as credit in the world, and reputation among men of science. He was a voluminous writer; he had much learning and sagacity, but he often wanted precision in his language and his reasoning. In November 1(91, he had a paralytic attack, which terminated his scientific career, though he survived it till the 2d of April 1799, when a second stroke carried him off, at Héril, near Baieux. He was made, in the mean time, one of the 14+ original members of the National Institute, as a testimony to the merit of his past labours.

He had married, in 1763, Mlle, de Cussy, a lady of very respectable family in Normandy. He had three daughters; the first married Mr de Parfouru, who was an early victim of the Revolution; the second the celebrated Lagrange; and the third her uncle, Lemonnier the physician, who was also a man of considerable science, and a member of the Royal Society of London.

From 1735 to 1790, there are very few volumes of the Memoirs of the Academy without one or more of Lemonnier’s papers; but though not unimportant in the aggregate, they are somewhat uninteresting in the detail. They relate almost exclusively to astronomical observations; eclipses, occultations, appulses, oppositions, and conjunctions; solstices, longitudes and latitudes; with some accounts of astronomical instruments and apparatus. There are also some memoirs relating to the sun’s equation and diameter, and on his place, as compared with Arcturus; on the motion of Saturn, and on his fifth satellite; on the expansion of wooden measures; on the transit of Venus, and on the diameter and the tables of that planet; on Euler’s formula for parallax; on the variation of the needle; on lunar altitudes; on the tides; on horizontal refraction; on Saturn’s ring; and on some currents of wind. He also published separately some extensive works, which acquired considerable celebrity.

1. The first was his Histoire Celeste, 4to, 1741, comprehending the interval from 1666 to 1685, and containing an account of a transit instrument of Graham’s construction.

2. Théorie des Comètes, 1743, in 8vo, including a translation of Halley’s work on comets, together with a method of computing the orbit from three observations.

3. Institutions Astronomiques, 4to, 1746; an improved translation of Keill’s Astronomy, which long continued to be the best elementary treatise in the French language. It contains also solar tables, and a variety of other additions derived from observation.

4. Observations Astronomiques, part i. 1751; ii. 1754; iii. 1759; iv. 1775.

5. A Letter on the Theory of the Winds, in Halley’s Tables, published by Chappe.

6. Nouveau Zodiaque, réduit à 1755, Paris, 1755, in 8vo, containing thirty-one pages of charts, much more complete than those of Senex, and superseded by some very late publications only.

7. A History of Astronomy in the Traité d’Aberration of Fontaine des Crutes.

8. Observations pour la Mesure du degré entre Paris et Amiens, 8vo, 1757.

9. Abrégé du Pilotage, par Goubert, 1766, in 4to, with additions.

10. Astronomie Nautique Lunaire, 8vo, 1771.

11. Exposition des Moyens les plus faciles de résoudre plusieurs questions dans l’Art de la Navigation, 1772, in 8vo, employing very generally a table of verse sines, and greatly recommending the use of Gunter’s scale for nautical computations.

12. Essai sur les Marées, 1774, in 8vo, particularly describing the effects of the tides at Mont St Michel, and on the neighbouring flat sands, and including also some considerations on refraction, and on magnetism.

13. Description et Usage des principaux Instrumens d’Astronomie, 1774, folio, forming part of the collection of Arts et Metiers.

14. Atlas celeste de Flamsteed, 1776, in 4to, revised.

15. Lois du Magnétisme, 2 parts, 8vo, 1776-8, with an elaborate chart.

16. Traité de la Construction de Vaisseaux, par Chapman, 1779, folio, from the Swedish, and said to be less perfect than the translation of Vial du Clairbois.

17. Mémoires concernant diverses questions d’Astronomie et de Physique, 4 parts, 1781-4-6-8, in 4to.

18. De la Correction introduite pour accourcir la Ligne sèche du Lock de dix-huit pieds, 8vo, 1790.

19. Lettre au sujet d’une Eclipse, Par. 1791; together with some remarks on navigation, and on the cur [7:13:228]rents of the South Seas, all apparently from the Memoirs of the Academy. The eclipse, which was observed as annular in China, should have been total, according to the computed distance of the luminaries concerned.