Paper, 'Note on the necessity of using well-annealed and homo­geneous glass for the mirrors of telescopes' by Andrew Ainslie Common Common writes: 'In 1880 I ordered of the St. Gobain Glassworks, through their London agent, M. de Grand Ry, a disk of glass for the mirror of a 5-foot telescope. The limit of weight imposed by the manufacturers permitted a disk of about 61 inches diameter and 5 inches thickness ; this was made with a hole through the middle of 10 inches, in order to enable the telescope to be used as a Cassegrain telescope if required.' Annotations in pencil and ink. Subject: Optics / Scientific apparatus and instruments Received 18 November 1891. Read 10 December 1891. A version of this paper was published in volume 50 of the Proceedings of the Royal Society as 'Note on the necessity of using well-annealed and homo­geneous glass for the mirrors of telescopes'. 1891