Picard did not conceive the method of measuring a celestial body's right ascension by recording the time at which the body crossed the observer’s meridian. According to French astronomer Camille Guillaume Bigourdan (1851-1932), the French astronomers Adrien Auzout (1622-1691) and Jacques Buot (or Buhot) (<1623-1678), the Dutch physicist Christiaan Huygens (1629-1695), the Czech physician/astronomer Hagecius (1525-1600) had all suggested the method; even the ancient Greek astronomer Hipparchus (190 B.C.E.-120 B.C.E.) had hinted at it. However, the method had never been put into practice because it required both a telescope in place of the traditional sight of a quadrant and a very accurate clock. Picard was the first astronomer to actually employ the method. [G. Bigourdan (1917) "Sur l'emplacement et les coordonées de l'Observatoire de la porte Montmartre" (On the site and coordinates of the observatory by the Montmartre gate), Comptes rendus, vol. 164, pages 537-543.]
In October 1669, Picard sent, to the Royal Academy of Sciences in Paris, a report of his celestial observations during the preceding year, which included the observation of two bright stars, Regulus and Arcturus, while the sun was still in the sky. The report was recorded in the Registres des Procès-verbaux de l‘Académie des Sciences. On reading the report, it becomes apparent that Picard had been using clocks to determine the right ascension of stars. French astronomer Pierre Charles Le Monnier (1715-1799) records an extract of Picard’s report and then remarks:
"Cette Observation est remarquable, étant inoüi qu'on eût jamais pris la Hauteur Méridienne des Etoiles fixes non seulment en plein Soleil, mais pas même encore dans la force du Crépuscle; desorte qu'il est maintenant facile (continue M. Picard) de trouver immédiatement les Ascensions droites des Etoiles fixes non seulment par les Horloges à Pendule, mais aussi par l'Observation du Vertical du Soleil au mème temps qu'on observera la hauteur Méridienne d'une Etoile fixe."
(This observation is remarkable, it being unheard of that one has ever taken the meridian altitude of fixed stars not only in full sun, but still not in the force of twilight; so it is now easy (continues Mr. Picard) to find immediately the right ascensions of the fixed stars not only by pendulum clocks but also by observation of the vertical of the sun at the same time that one observes the meridian altitude of a fixed star.) [Pierre-Charles Le Monnier, Histoire céleste, ou Recueil de toutes les observations astronomiques faites par ordre du Roi … (Paris, France: Briasson, 1741), page 40.]
biodiversitylibrary.org
Picard, Jean (1729). "Voyage d'Uranibourg, ou observations astronomiques faites en Dannemarck" [Uranibourg voyage or astronomical observations made in Denmark]. Mémoires de l'Académie royale des sciences (in French). 7: 193–230. From pp. 215-216: Picard stated that Tycho couldn't accurately determine the position of Polaris because he lacked a telescope. However "… il y a un obstacle de la part de l'Etoile Polaire … paroît plus proche de Pole d'environ 20" qu'elle n'étoit un an auparavant." ( … there is an obstacle on the part of the star Polaris, which from one season to another suffers certain variations that Tycho had not noticed, and that I've observed for about ten years. That is, although the star Polaris annually approaches the pole by about 20", it happens nevertheless that towards the month of April the meridian height and the inferior height of that star become less by some seconds than it had appeared at the preceding winter solstice; instead, it should be greater by 5": then in the month of August and September its superior meridian height is found roughly such as it had been observed in winter, and even sometimes greater, although it should be diminished by 10 to 15"; but finally towards the end of a year, everything is compensated, such that Polaris appears closer to the pole by about 20" than it was a year before.) Picard concluded that the variation in the position of Polaris wasn't due to refraction by the atmosphere. However "… pour dire la verité, je n'ai encore rien pû m'imaginer qui me satisfît là-dessus …" ( … to tell the truth, I still couldn't imagine anything that would satisfy me [regarding] that [i.e., the variations in the position of Polaris] … )
Picard did not conceive the method of measuring a celestial body's right ascension by recording the time at which the body crossed the observer’s meridian. According to French astronomer Camille Guillaume Bigourdan (1851-1932), the French astronomers Adrien Auzout (1622-1691) and Jacques Buot (or Buhot) (<1623-1678), the Dutch physicist Christiaan Huygens (1629-1695), the Czech physician/astronomer Hagecius (1525-1600) had all suggested the method; even the ancient Greek astronomer Hipparchus (190 B.C.E.-120 B.C.E.) had hinted at it. However, the method had never been put into practice because it required both a telescope in place of the traditional sight of a quadrant and a very accurate clock. Picard was the first astronomer to actually employ the method. [G. Bigourdan (1917) "Sur l'emplacement et les coordonées de l'Observatoire de la porte Montmartre" (On the site and coordinates of the observatory by the Montmartre gate), Comptes rendus, vol. 164, pages 537-543.]
In October 1669, Picard sent, to the Royal Academy of Sciences in Paris, a report of his celestial observations during the preceding year, which included the observation of two bright stars, Regulus and Arcturus, while the sun was still in the sky. The report was recorded in the Registres des Procès-verbaux de l‘Académie des Sciences. On reading the report, it becomes apparent that Picard had been using clocks to determine the right ascension of stars. French astronomer Pierre Charles Le Monnier (1715-1799) records an extract of Picard’s report and then remarks:
"Cette Observation est remarquable, étant inoüi qu'on eût jamais pris la Hauteur Méridienne des Etoiles fixes non seulment en plein Soleil, mais pas même encore dans la force du Crépuscle; desorte qu'il est maintenant facile (continue M. Picard) de trouver immédiatement les Ascensions droites des Etoiles fixes non seulment par les Horloges à Pendule, mais aussi par l'Observation du Vertical du Soleil au mème temps qu'on observera la hauteur Méridienne d'une Etoile fixe."
(This observation is remarkable, it being unheard of that one has ever taken the meridian altitude of fixed stars not only in full sun, but still not in the force of twilight; so it is now easy (continues Mr. Picard) to find immediately the right ascensions of the fixed stars not only by pendulum clocks but also by observation of the vertical of the sun at the same time that one observes the meridian altitude of a fixed star.) [Pierre-Charles Le Monnier, Histoire céleste, ou Recueil de toutes les observations astronomiques faites par ordre du Roi … (Paris, France: Briasson, 1741), page 40.]
