Jean Gabriel Augustin CHEVALLIER (1778-1848) known as "l'Ingénieur Chevallier", optician, manufacturer of microscopes, optical instruments and spectacles. Manuscript signed "L'Ingr. Chevallier", Météorologie, Paris 1818 4 pages in-4 on his letterhead J.G.A. Chevallier, Ingénieur-Opticien de S.A.R. Monsieur Frère du Roi, des Princes, et du Garde-Meuble de la Couronne ; Membre de la Société Royale Académique des Sciences de Paris, etc. and vignette with royal oars. Interesting account of Meteorology, a science that is not yet quite a science... "For a long time, Meteorology, associated with the absurd dreams of judicial Astrology, offered in the perturbations of the atmosphere, only a ridiculous consequence of the influence attributed to the Asters on this terrestrial envelope, and of the occult causes by means of which it was then claimed to explain all phenomena and to solve all the difficulties of physics. At that time there were no fixed data that could be taken as a starting point, no reasoned plan of observations, no instrument to which they could be related or which would allow them to be discussed, compared with each other, and to draw reliable conclusions"... He reviews the history of this discipline, which is closely linked to the discoveries and invention of new scientific instruments for observation and measurement, which became increasingly precise and efficient, leading to more reliable results that influenced many fields, including medicine, agriculture and physics. Finally, he returns to the important work of the famous Cotte, who made it possible to forecast the weather for the first three months of 1819, which he details... If these facts might be of interest to the readers of his correspondents, he authorises them to "insert my letter in your paper"... A handwritten weather bulletin from him for 4 August 1818 is attached.