Geometrical researches on the theory of parallels
Nikolai Lobachevsky's 1840 treatise founding non-Euclidean geometry, translated from the German by George Bruce Halsted and issued by the Open Court Publishing Company of Chicago in 1914 for mathematicians and students. The eighteen figures are spare line diagrams printed from woodblocks: labelled points, rays running off to parallel limits, triangles and angle arcs, usable as stark black-on-white geometric marks or as period mathematical ornament.
