Correspondence with Cameron Dinwoodie on many topics concerning the British Astronomical Association Computing Section, including the satellites of Jupiter and Saturn; the application of electronic computers to the calculation of planetary ephemerides; lunar and solar eclipse and lunar occultation calculations; the B.A.A. Handbook and the material to be used therein; the policy of the Computing Section and the division of the work amongst the computers; and the conferral of the Freedom of the Burgh of Langholm on Neil Armstrong on 11 March 1972. There are letters received from the Dinwoodie's family after his death, including Dinwoodie's notes on his life history, as dictated to Mrs Dinwoodie. There is also a draft of Porter's obituary notice for the 'Journal of the British Astronomical Association' (1979).