Copy letter from Herbert Rix, to Professor William Edward Ayrton, Fellow of the Royal Society 'Dear Sir, Before getting estimates for the figures illustrating the paper by yourself & Mr Kilgour, I should like to have your views as to which shd [should] be done on wood to go in the text, & which shd be lithographed as plates. If you wd [would] call & see me about them it wd be perhaps the most satisfactory way of coming to a clear understanding. Yours truly Herbert Rix Asst Sec RS [Assistant Secretary, Royal Society]'. 10 December 1891