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‎Astronomie populaire publié d'après son ordre sous la direction de M. J.A. Barral -- EDITION ORIGINALE -- BEL EXEMPLAIRE -- 4 VOLUMES (COMPLETE SET°‎

‎P., Gide, 1856/1858; 4 volumes in 8 reliés en demi-chagrin vert, dos ornés de fers dorés (reliures de l'époque), (mouillures pâles dans l'angle extérieur à quelques feuillets du tome 3), T.1 : (2), 12pp., 559pp., T.2 : (2), 554pp., T.3 : (2), 635pp., T.4 : (2), 854pp., PLANCHES hors texte, figures dans le texte‎

‎---- EDITION ORIGINALE ---- BEL EXEMPLAIRE ---- " Arago was concerned with optical instruments that proved useful for a variety of purposes, in physics and meteorology as well as in astronomy, for which they were mainly devised. In 1811, he invented the polariscope to determine the degree of polarization of light rays by passing them successively through a mica or rock-crystal polarizer and an Iceland spar analyzer... He transformed it into a polarimeter which he used to verify one of the few mathematically expressed laws he discovered... In 1815, he built a primitive cyanometer to measure the degree of blueness of the atmosphere. In 1833, he proposed a photometer to measure comparative intensities of stellar light. He also perfected an ocular micrometer for measuring small angles, which was erroneously attributed to William Pearson. The workings of all these instruments, based upon polarization phenomena, were expounded with great clarity and enthusiasm in Arago's public lectures at the observatory, published posthumously as Astronomie populaire". (DSB I p. 202)**139.L4‎