CLAIRAUT, (ALEXIS CLAUDE de). - THE FIRST DIRECT CONFIRMATION OF THE COPERNICAN THEORY.

De L'Abberation apparente des Etoiles, causée par le mouvement progressif de la Lumière.

(Paris, L'Imprimerie Royale, 1740). 4to. Without wrappers. Extracted from "Mémoires de l'Academie des Sciences. Année 1737". Pp. 205-227 a. 2 folded engraved plates.

First appearance of this extremely importent paper in which Clairaut directly confirms the rotation and the orbital movement of the Earth around the Sun, and giving an indirect proof of the axiom, that the velocity of light does not depend on whether the light source moves away or toward the observer. The Earth does move after all !!

In 1728 James Bradley, trying to measure the stellar parallax, discovered stellar aberration - the angular displacement of the apparent direction of starlight due to the earth's motion - and attributed it to the combined effect of the finite velocity of light and the earth's orbital velocity. But Bradley had not given any theoretical proof, but Clairaut did in the offered paper.

Aberration is "the apparent change in direction of a source of light caused by an observers component of motion perpendicular to the impinging rays. During this time the telescope has moved a short distance, causing the photons to reach a spot on the focal plane, displayed from the former image position... This discovery provided the first direct physical confirmation of the Copernican theory. A second importent application of aberration has been its clear-cut demonstration that, as is axiomatic to special relativity, light reaching the earth has a velocity unaffected by the relative motion of the source toward or away from earth."(McGraw-Hill "Concise Encyclopedia...").

Order-nr.: 46843