French Geodesy in 19th and 20th Centuries. Context, actors and mathematical practices on the field
Résumé
Geodesy in the nineteenth century was a branch of astronomy concerned
with the determination of the mathematical figure of the Earth, but also
with questions of earth-science (cartography, geology and geophysics). This
science played a crucial role in military and colonial endeavors, and
provides an example of the way in which mathematical techniques were
developed and mobilized in the service of the state.
Who were the main practitioners of 19th-century geodesy, and what
significance should we attribute to geodetic operations, such as the
measurement of a meridian or parallel arc, or the determination of the
astronomical position of geodetic stations? Geodesists were often not
scientists but military officers, and historians have tended to treat
them as followers rather than innovators.
I will examine examples of geodesy as material and theoretical knowledge
mobilized in the field or developed in scientific institutions such as
the French Bureau des longitudes, where academicians, military officers
and precision instrument makers worked together. One of the Bureau's
directors, Henri Poincaré, considered geodesy to be useful for the
French State, not only for cartography, but also for the general
education of students at the Ecole polytechnique. Poincaré also helped
determine latitudes, the gravitational constant, and the nature of
gravitational action.
On a larger scale, my aim is to illuminate the evolutions in geodetic
science before WWI.