Geometrical Optics

YOUR correspondent “P. C.” (NATURE, vol. xxii. p. 607) asks information concerning a work, in English or French, on geometrical optics, thoroughly explaining the optical construction of telescopes and microscopes. I am not aware of any such publication these last forty years, but deem it possible that it may interest your correspondent to know of the existence of such a work in German by von Littrow, entitled “Dioptrik, oder Anleitung zur Verfertigung der Fernröhre.” It was published, I believe, in Vienna about 1838.