821 



PICARD, JEAN. 



PICARD, LOUIS BENOIT. 



of the Tropical Year ' (Id., tome xiii.) ; 8, ' On the Proper Motion of 

 the Fixed Stars' ('Mem. de 1'Inet. Nat. Ital.,' tome i); 9, 'The 

 Metrical System for Sicily,' 1812; 10, ' Lessons in Astronomy," 1817; 

 11, 'On the Observed and Calculated Solstices' ('Mem. de Tlnst. de 

 Milan,' tome ii.); 12, 'On the Italian and European Clock '(' Qiorn. 

 de Scienze par la Sicilia, Aug., 1824); 13, 'On the Progress of 

 Astronomy ' (' Giorn. de Soc. Lett, et Arti par la Sicilia,' April, 1824) ; 

 14, ' Description of the Meridian of the Cathedral of Palermo, established 

 by Piazzi in 1798,' by M. Cacciatore (Id., August, 1824). 



PICAKD, JEAN, was born 21st July, 1629, at La Fleche in the 

 present department of the Sarthe, and became priest and prior of 

 Rillo in the same department. Scarcely anything is known of his 

 early history. Even the names of his parents appear to have been 

 forgotten, as they are not mentioned by Lalande, who visited his birth- 

 place. Pezenas, in his ' Critical History of the Discovery of the Lon- 

 gitude,' referred to by Delambre, speaks of one Picard, a gardener of 

 the Duke of Crequi, whom the astronomer Le Valois instructed so 

 successfully in the use of astronomical instruments, that he became 

 one of the most celebrated observers of his age. As the subject of 

 this article is the only Picard who is known to have acquired any 

 celebrity as an astronomical observer, it may be conjectured that he 

 was the humble individual here alluded to. The earliest event with 

 which his name is associated, and of which the date is recorded, is the 

 solar eclipse of the 25th August, 1645, which he observed with the 

 astronomer Gassendi, whom he succeeded, in 1655, as professor of astro- 

 nomy in the College Royal of France. He was one of the eight 

 individuals selected by Colbert, in 1666, to originate the Academy of 

 Sciences. The following year he made his first application of the 

 telescope to the measurement of angles ; which alone, observes Delarn- 

 bre, would entitle him to the esteem and remembrance of astronomers. 

 Prior to this, plain sights only had been used, with which not only are 

 distant objects frequently altogether invisible, but of those which can 

 be seen the outline is seldom distinctly defined, while in some cases, as 

 in the fixed stars, they have an apparent magnitude which they do not 

 really pos*ess. According to Lahire however the merit of this great 

 improvement (which was eagerly adopted by every astronomer of 

 note, Hevelius excepted) is divided between Picard and Auzout, who 

 were in partner-hip, though, from Picard's description of his inven- 

 tion, in Ms work entitled ' Figure de la Terre.' it would appear to be 

 exclusively due to himself. Soon after this he introduced an entirely 

 new system of astronomical observations, wherein the pendulum, then 

 recently invented by Huyghenr, is first brought into use in determin- 

 in-' the right ascension of the stars by noting the instant of their 

 passage across the meridian. This method, observes Delambre, which 

 ia adhered to at the present day, "insures to those two authors, 

 Huyghens and Picard, an incontestable superiority over all the astro- 

 nomers of the time without a single exception." In the memoir 

 wherein these views are more fully developed, and which he read 

 before the Academy of Sciences, in April 1670, he urges the necessity 

 of forming more correct tables of the sun and fixed stars, as also 

 tables of refraction, which he regarded as the chief foundation of all 

 sound practical astronomy. For this purpose he solicited the erection 

 of n mural quadrant, which after many years of needless delay was 

 finally adjusted in the plane of the meridian, not however till Picard 

 was upon his death- bed. 



In 1671, with a view of giving astronomers greater confidence in 

 employing the observations of Tycho Brahd, Picard visited the island 

 of Hocne in order to determine the position of Uraniberg. Scarcely 

 a vestige of the observatory remained ; sufficient however to enable 

 him to detect an error of one minute in the latitude and several 

 minutes in the longitude, as given by Tycho, which confirmed the 

 suspicions previously entertained by astronomers. While absent on 

 this occasion he met with Roemer, then a young man, with whose 

 mathematical talents he was so well pleased that he brought him to 

 Paris and introduced him to the academy. The observatory of Paris, 

 the plan of which had been furnished by Picard, was completed in 

 1671, when it was immediately occupied by Dominic Cassini, who, at 

 Picard's recommendation, had been invited by Colbert to take up bis 

 residence in France. It was not till two years later that inferior 

 accommodation within the same building was allotted to Picard, "He 

 saw,"' says Dclambre, " all his projects neglected or their execution 

 deferred ; all expenditure and encouragement lavished upon objects of 

 less utility, though to the eye of the vulgar of a more brilliant character, 

 such as the rotation of the three- planets, and the four new satellites 

 of Saturn ; while telescopes of great cost were imported from Italy to 

 verify these discoveries, which, though certainly very curious, were 

 and always will be useless." The astronomical ephemeris entitled 

 ' La Connaitsance des Temps,' originated with Picard in 1679, and was 

 continued by him till his death. The same ye.;r he was nominated 

 with Lahire, by the king, to conduct certain surveys along the coast of 

 Gaycony, the result of which sufficiently indicated the necessity of 

 constructing an entirely new map of the country. For this purpose 

 he proposed the extension of the arc of the meridian passing through 

 the Paris observatory as far as the extremities of the kingdom : a 

 proposal which has since been carried into effect. As an observer, he 

 was no less industrious and accurate than, as a philosopher, he was 

 enlightened. His observations from 1666 to 1682, collected and 

 published by Lemonnier in 1741, under the title of 'liistoire Celeste,' 



are a sufficient proof of his activity ; while his perseverance for ten 

 years in observing the minute variations which, from causes then 

 unknown, are continually taking place in the altitude of the polar star, 

 is equally conclusive as to his zeal and the perfection which astrono- 

 mical observation attained in his hand. 



What Picard is however now chiefly remembered for, is his measure- 

 ment of an arc of the meridian of Paris between Amiens and Malvoisine. 

 This was begun in 1669, and forms the subject of his work entitled 

 'Mesure de la Terre,' Paris, 1671, a large folio of 30 pages. The base 

 extended along a paved road from Villejuive to Juvisy ; it was twice 

 measured, the results being 5662| and 56tf3i toises, the mean of which 

 was taken. The difference between the latitudes ft Amiens and 

 Malvoisine he found to be 1 22' 55", and the length of the inter- 

 mediate arc 78,850 toises; whence it followed that the length of one 

 degree between those latitudes was 57,067. The toise employed was 

 that of Chastelet. " Lest," says Picard, " this toise should share the 

 fate of those employed in former surveys, of which only the name 

 remains [it has since been lost], we will connect it with a measure 

 which, being taken from nature herself, must te invariable and uni- 

 versal." He then states that he determined with great care the length 

 of the pendulum vibrating seconds (which he supposd was constant 

 for all latitudes), and which, at Paris he found to be 440'5 ligues, 

 according to the toise of Chastelet. ('MiSsure de la Terre,' p. 4.) 

 The most accurate determinations which have since been made do not" 

 differ from this result by so much as the ^ of a ligne. (Fraucoeur, 

 ' GiSomorphie," p. 256.) At the date of this survey the law of refrac- 

 tion was imperfectly known, and its effects were neglected. The effects 

 arising from what have since been termed aberration and nutation had 

 been felt, but astronomers then, and for ntore than half a century 

 afterwards, knew not how the requisite corrections should be applied. 

 These were therefore sources of error which vitiated the observations 

 of Picard in common with those of all other astronomers of that 

 time; and in addition an error of six toises was committed in the 

 measurement of the base. The whole of the operations have since 

 been repeated by Lemonnier ('Degrd du Meridieu,' Paris, 8vo, 1740) 

 and Lacaille, and still more recently by Delambre. The final result 

 gives 57,074 toises for the length of the degree, which differs from 

 Picard's by 17 toises (35 '6 English feet); and, thus rectified, this 

 measurement is one of those on which the greatest relinuce is now 

 placed. The care with which the whole of Picard's operations were 

 conducted, and the superiority of his instruments and methods over 

 those employed in any previous survey, naturally produced consi- 

 derable confidence in his result. Astronomers would not indeed have 

 been justified had they regarded the results of former surveys in any 

 other light than rough approximations which enabled them to assign 

 the limits within which the true dimensions of the earth would one 

 day be found, but which were useless in determining what its dimen- 

 sions and figure really were. Newton, in 1666, failed to establish the 

 truth of his theory of gravitation by employing an erroneous measure 

 of the earth's radius, and did not resume its consideration till he 

 heard of Picard's survey, by which it was confirmed. Norwood's 

 measurement of the arc of the meridian between London aud York, 

 which took place in 1633, gave results which have since been shown 

 to be correct, and were doubtless known to Newton. But his measure- 

 ment differed too considerably from those which preceded it to be 

 admitted on the strength of the imperfect apparatus employed by 

 him. Norwood's measure is called by Delambre a great piece of good 

 fortune. [NORWOOD, RICHARD.] 



Picard died at Paris, 12th of July, 1682 (Delambre); according to 

 other authorities, his death took place in 1683 or 1684. Besides the 

 works already mentioned, the following are inserted in the 'Memoirs' 

 of the Academy of Sciences. The numbers refer to the volume : 

 vi, De la Pratique des Grands Cadrans par le Calcul ; De Mensuris ; 

 De Mensura Liquidorum et Aridorum ; De Proportione Aquarum 

 Effluentium; Fragments on Dioptrics ; Treatise on Levelling. All but 

 the last are in the 'Divers Ouvrages,' &c., folio, Paris, 1693. vii, 

 Measurement of the Earth ; Astronomical Observations made in 

 Denmark ; Astronomical Observations made in various parts of France 

 (4 papers), x, Immersion and Emersion of Jupiter's Satellites 

 observed at Paris in 1668; Observation of the Lunar Eclipses of 7th 

 July, 1675, and llth January, 1676, by Cassiui, Picard, Roemer (2 

 papers); Experiments relative to the Phenomenon observed in the 

 Vacuum of the Barometer; Occultation of Saturu by the Moon, 

 observed, by Cassini, Picard, Roemer, and De La Hire. 



(Delambre, A slronomie Moderne, and Biographic Ifnivendle ; Lalande, 

 Biographic Astronomique ; Coudorcet, Eloge de Picard; Fonteuelle, 

 Eloge de Picard ; Moutucla, Hist, des Mathematiques, Ac.) 



PICAKD, LODIS BENOIT, member of the French Academy, and 

 one of the most successful dramatists of his age, was born at Paris in 

 1769. His first production for the stage was ' Le Kadinage Dangereux,' 

 which was followed by a very long succession of comedies, displaying 

 novelty in their subjects, faithful and well hit-off portraitures of con- 

 temporary manners, playfulness of dialogue, and clever traits of satire ; 

 to such degree indeed that by some he has been styled the Moliere of 

 his day. Not only were his productions eminently popular at home, 

 but many of them were either translated or remodelled by Inland, 

 Hell, and other German writers. Among his pieces iu verse, ' Mediocre 

 et Rampant/ ' Le Mari Ambitieux,' and. ' Lea Ami* de College,' are 



