Correspondence with Airy and W.H.M. Christie concerning new astronomical techniques; requests for instruments and information; the testing of various instruments, such as a siderostat, telescopes and a driving clock; and the finding of the longitude. The correspondents include W. De La Rue, W. Huggins, S.P. Langley, Sir R.S. Ball, R.L.J. Ellery, E.K. Abbe, H.H. Turner and various lesser known scientists. There is a photograph of a negative of a plan of Flamsteed's equatorial sector, a photograph of a transit circle and six photographs of parts of a chronograph destined for Japan. The papers include material on Ertel's transit instrument; E.K. Abbe on settling time and longitude, written in German; and a translation into Spanish by J. Salozar of astronomical problems involving longitude.