Official and general correspondence, with related papers, regarding the design and finance of the Isaac Newton Telescope, including correspondence on the disk and glass; a letter from the Astronomer Royal to the Helwan Observatory, Egypt, 21 July 1947, regarding a large glass disk for the observatory's large reflector; correspondence with F.J. Hargreaves; a letter from the Astronomer Royal to the Director General of Observatories, New Delhi, 21 July 1947, regarding a large glass disk for the 100-inch reflector for India; letters concerning design development; correspondence with L.H.D. Pilkington concerning disks; correspondence on co-operation with Russia; correspondence on optical design; a graph from Pilkington Bros. showing ultra-violet and visible transmission curves of the experimental melt of BSC 518/641 and Schott UBK7; a graph from Pilkington Bros. showing the spectral transmission of stirred white plate; a graph by Dr Paul Wayman showing the largest image diameters accruing in the field of the Isaac Newton Telescope for different apertures of the connector plate; and drawings of the horizontal yoke telescope mounting.