LOBACHEVSKY, Nikolai (1792-1856). Sposob uviersitsia v izchezanii bezkonechnykh strok i priblizhatsia … [A method for ascertaining the convergence of infinite series …] in ‘Uchenya zapiski’, knizhka 2. Kazan: at the University, 1835.

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, in which the pioneer of non-euclidean geometry first gave ‘a rigorous definition of continuity and differentiability, and pointed out the difference between these notions’ (DSB). It also tackles infinite series (providing a new convergence criterion now known as ‘Lobachevsky’s test’), the problem of expressing functions by infinite products, and definite integrals. This issue of the Scientific Memoirs of Kazan University also contains the supplement to Zoographia Rosso-Asiatica , a study of animal species across Russia, and an article on ‘Buddhist cosmology’. Octavo (201 x 127mm). (Title skillfully repaired at gutter and outer margin, small stain to outer margin of the title.) Contemporary Russian green half leather, flat spine with blind-stamped lettering, green pebble cloth sides (spine chipped at extremities and rubbed with sporadic losses, joints cracked but holding, edges worn), preserving evidence of original wrappers in the inner margins of the title and last leaf. Provenance: some pencil underlining to the title.