François ARAGO (1786-1853). Autograph manuscript,... Lot 67

François ARAGO (1786-1853). Autograph manuscript, Parallaxe annuelle; 3 pages and a quarter in-fol. with erasures and corrections. Interesting scientific study on the movement and position of the stars, illustrated with a sketch. Arago has drawn a sketch at the head, which he comments on: "Let ABDF be the contour of the ecliptic, which I assume to be circular, and E a star. If we imagine that the observer is placed at any point G situated on this contour and that from G and center C, we lead two lines CE and GE to the star E, the angle CEG which they form between them, will be the parallax of the star for the current position of the observer, because CEG is the angle under which the radius CG of the terrestrial orbit is seen from E"... Etc. "To judge the nature of the displacement that the star will appear to experience, we can therefore disregard translational motion, assume the earth to be motionless, as it appears to be, and lead through the place that the observer occupies, a set of visual rays placed in relation to the reference line as observation will have presented them. These visual rays will therefore be parallel to the true rays GE, GE, GE, &c in whose direction the star had been successively observed"... The manuscript is authenticated at the end by Ernest Laugier, of the Académie des Sciences (1812-1872).