Paper, 'Terrestrial refraction in the Western Himalayan Mountains' by James Thomas Walker Walker writes: 'In the operations of the Great Trigonometrical Survey of India it is customary to determine the coefficient of refraction by reciprocal vertical observations between contiguous stations on the sides of all the principal triangles, and also as many as possible of the secondary triangles.' Annotations in pencil and ink. Subject: Optics Received 13 January 1894. Read 1 March 1894. A version of this paper was published in volume 55 of the Proceedings of the Royal Society as 'Terrestrial refraction in the Western Himalayan Mountains'. 12 January 1894