Copy letter from Herbert Rix, to Professor Joseph John Thomson, Fellow of the Royal Society 'Dear Sir, We return today (registered) Mr Burbury's paper. We are obliged to you for sending it promptly for use at the meeting. It came, however, in rather a perilous manner, unregistered [underlined], & with the postal wrapper burst. When you finally send it back to us, please register it. We sent stamps for this purpose when we first forwarded you the MS. [manuscript]. Yours truly Herbert Rix Asst Sec RS [Assistant Secretary, Royal Society]'. 20 November 1891