Copyright: Collections École Polytechnique
The cyanopolarimeter, presented by François Arago to the Academy of Sciences, was manufactured by Jean-Baptiste Soleil according to the astronomer and physicist's instructions. This instrument was used to measure the angular rotation of the electric field of linearly polarized light induced by passing through a liquid or solid substance. It was used to calculate the optical rotation power of the analyzed sample. With this polarimeter, François Arago determined that the sun is neither solid nor liquid, but made up of an incandescent gas.