Copy letter from Robert William Frederick Harrison to Colonel Sir David Bruce CB, FRS 'We are now printing Mr Buchnan's paper communicated by you, and for the plate we are proposing to try 3-colour process, in order to save money and time. It will cost only half and be done in half the time. We are getting a quantity of coloured plates now and have to consider economy in reproduction. 3-colour process is a photographic facsimile process and I think it will give satisfaction. we are not undertaking it without due consideration. Tje Engravers assure us the subject is suitable. You will find a 3-colour plate at Proc[eedings of the Royal Society] B 561, PI 9 (Nov 26 1910). I think you will be satisfied with the result, but did not care to go forward without first apprising you.' 2 June 1911