Mach (Ernst) Letter signed (‘E Mach’), in French, recipient unspecified, reply to invitation to write on optics declined as Mach found it difficult to write in French, reference to the French, German and English editions of his ‘History of Mechanics’ (1883), and to numerous articles on physics and the metaphysics of science, note recommending the young (and later influential) engineer Peter Klementich de Engelmeyer, then in Moscow, margins slightly browned, little thumbing or dust-soiling to corners, faint interlinear inscription in blue crayon to recto of first leaf, tall 8vo, Vienna, 1 March 1897.