A posse, ad esse, ad eundem

Art:The 17th-century French astronomer Jean Picard made the first accurate measurement of the distance between two French cities by means of triangulation. In a book on Earth measurement, published in 1671, Picard gave the figure for 1 degree of longitude, from which he computed the size of the Earth.

from being able, to being, to the same


“My days I devote to reading and experiments in chemistry, and I spend many of the clear nights in the study of astronomy. There is, though I do not know how there is or why there is, a sense of infinite peace and protection in the glittering hosts of heaven. There it must be, I think, in the vast and eternal laws of matter, and not in the daily cares and sins and troubles of men, that whatever is more than animal within us must find its solace and its hope.”

H.G. Wells, The Island of Dr. Moreau


Please…listen whilst you ponder:





The Short End Of It:

Jean Picard

French astronomer who first accurately measured the length of a degree of a meridian (longitude line) and from that computed the size of the Earth.

Picard became professor of astronomy at the Collège de France, Paris, in 1655. His measurement of the Earth was used by Sir Isaac Newton to verify his theory of gravitation. In 1671 Picard went to the observatory of the noted 16th-century Danish astronomer Tycho Brahe at Hven Island, Sweden, to determine its exact location so that Brahe’s observations could be more precisely compared with those made elsewhere. He brought back copies of the originals of Brahe’s principal work.

Picard is also credited with the introduction of telescopic sights and the use of pendulum clocks as contributions to greater precision in astronomical observations. In 1675 he made the first recorded observation of barometric light, the light that appears in the vacuum above the mercury in a barometer when the barometer is moved about. In 1679 he founded and became editor of La Connaissance des temps ou des mouvements célestes (“Knowledge of Time or the Celestial Motions”), the first national astronomical ephemeris, or collection of tables giving the positions of celestial bodies at regular intervals.


Mesure de la terre [par l'abbé Picard]


The Longer (and better) End Of It:


As per the Galileo Project:

Picard, Jean

1. Dates
Born: La Fl�che, 21 July 1620
Died: Paris, 12 October 1682
Dateinfo: Dates Certain
Lifespan: 62
2. Father
Occupation: Pub
Picard’s father was almost certainly Jean Picard, a bookseller in La Fl�che; possibly I should consider him a small merchant in a provincial town, but I am listing everyone connected with the book trade under “Pub.” Nothing is known of Picard’s youth.
No information on financial status.
3. Nationality
Birth: French
Career: French
Death: French
4. Education
Schooling: Paris, M.A.
Picard probably did his early studies at the Jesuit college at La Fl�che. Considerably later he earned an M.A. from Paris is 1650. As usual, I assume a B.A. There is no indication of what he did between La Fl�che and his studies in Paris, a period of about twelve years.
5. Religion
Affiliation: Catholic
Picard was ordained a priest in 1650. He held at least four benefices.
6. Scientific Disciplines
Primary: Astronomy, Cartography, Instrumentation
Subordinate: Physics, Optics, Hydraulics
The usual story of Picard is that he was the gardener of the Duke of Crequi. Jacques de Valois, having met Picard, inspired him to make astronomical observations. The Picolet volume demonstrates that this story is not true.
Picard became very involved in astronomy and made observations with Gassendi in Paris in the period 1645 to 1652. With Auzout he perfected the movable-wire micrometer and utilized it to measure the diameter of the sun, moon, and planets. In 1667 Picard applied the astronomical telescope to the quadrant and the sector expanding their usefulness in observations. He made other innovations in instrumentation as well.
Picard became an important member of the group of academiciens carrying out cartographic measurements. He was placed in charge first of making a map of the region of Paris and then of the operation to remeasure an arc of the meridian. He utilized Snell’s method of triangulation. His method and measurements were the topic of his Mesure de la terre (1671). He was also an important member of the team that began to compile a map of France based on scientific principles. He was a major figure in the development of scientific cartography.
In 1673 he was at the Paris observatory collaborating with Cassini, Roemer, and La Hire on the institute’s regular project of observations.
Picard directed his attention to other projects of the Acad�mie such as the surveying operations at Marly and Versailles, the whole problem of supplying Versailles with water (a project in which he was central) and barometric experiments and other topics of physics. He left behind papers on hydraulics.
Picard was also skilled in optics. He made suggestions to improve the telescope and left behind manuscripts on dioptrics.
7. Means of Support
Primary: Government, Church Life
Secondary: Academia
There is some evidence to suggest that Picard taught in the University of Paris during the 1650’s, but his life during this period is very obscure.
Picard was apparently not one of the founding members of the Acad�mie in 1666. However, he was appointed in 1667 with a pension of 1200 livres, raised to 1500 in 1669. From that time he spent his entire career devoted to Acad�mie projects.
When He died, Picard held two priories and two other minor benefices, all four of them in his native Anjou. Although the exact dates have not been established, he received one of the priories (worth about 400 livres per annum) about 1661, and the other (worth about 300 livres per annum) between 1661 and 1675. The two minor benefices were worth about 100 livres together. Picolet concludes that Picard had an income of between 700 and 1000 livres in addition to his pension from the Acadmie.
8. Patronage
Types: Eccesiastic Official, Scientist
In 1664 Picard was the confidant of Abb� de Richelieu (a great-nephew of the Cardinal), and there is good cause to believe that he received at least one of his benefices from the Abb�.
Olmstead offers convincing evidence that Auzout, who was a well established astronomer at the time, was directly responsible for Picard’s appointment to the Acad�mie.
9. Technological Involvement
Types: Instruments, Cartography, Hydraulics
With Auzout, he perfected the movable-wire micrometer. He was the one who incorporated the astronomical telescope into surveying instruments such as the quadrant and sector. He also developed a new leveling instrument (also with telescope attached) that remained the standard one used in leveling for a long time.
He was the central figure in planning and implementing the water supply for the fountains at Versailles.
10. Scientific Societies
Memberships: Académie Royal des Sciences, 1666-82
Picard was not a founding member of the Acad�mie but was added soon after its establishment.
He corresponded directly or indirectly with Erasmus Bartholin, Johan Blaeu, Martin Fogel, Michel Antoine Hacki, Johann Hevelius, Jan Hudde, Lodewijk Huygens, Stanislaus Lubieniecki de Roles, Andreas Spole, and Jules Reichelt. His correspondence with Hevelius (on telescopic sights) has been published.



 to continue reading (a dismal fraction) , Mesure de la terre 1671 (albeit en francais):



A petite side note  very worth mentioning:


From Darkness at Night:

The French astronomer, Jean Picard , after an expedition to determine the longitude of Tycho Brahe’s old observatory on the Island of Hveen, returned to Paris in 1672 accompanied by the young Danish astronomer Ole Roemer.  Roemer was appointed tutor to the Dauphin and assigned the task of assisting in updating the occultation records of Jupiter’s moons.  Like Cassini, Roemer  noticed the irregularities in Io’s eclipses.  The satellite’s immersions(disappearances) behind Jupiter and emersions(reappearances) rarely occurred precisely on time.  With improved data, he became convinced that finiteness of the speed of light explained these variations.  In September, 1676, he announced at a meeting of the Paris Academy of Sciences that the eclipse of Io on November 9 would occur  10 min later.  He went around repeating this prediction, explaining that the earth was moving away from Jupiter, and the delay would be caused by the extra distance light had to travel to catch up with the Earth.  His successful prediction, followed by his paper read before the Academy, established him as the discoverer of the finite speed of light.  He pointed out that the change that had occurred in Io’s orbital period, though “not sensible in two revolutions, became very considerable in many taken together.”

Five years later, o returning to Copenhagen, Roemer was appointed a professor at the university; he became mayor of Copenhagen, and then astronomer royal of Denmark.  Among his many inventions must be included the mercury thermometer in the from used nowadays.  Gabriel Fahrenheit, a German-Dutch instrument maker, only copied Roemer’s method of construction and calibration (ice at 32 degrees and boiling water at sea level at 212 degrees); the misnamed Fahrenheit thermometer should be called the Roemer thermometer.


 Please take some time to do your own research on this fascinating man.






Author: mmartel

"If he's honest, he'll steal; if he's human, he'll murder; if he's faithful, he'll deceive. Being at a loss to resolve these questions, I am resolved to leave them without any resolution." I have so much to say to you that I am afraid I shall tell you nothing."

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