Copy letter from Herbert Rix, to Professor Walter Noel Hartley, [Fellow of the Royal Society] 'Dear Prof Hartley, Could you kindly remind me when and in what connection the two rollers of spectra were handed to us which you say on the corner of your MS [manuscript] "are in the possession of the Royal Society" Yours truly Herbert Rix Asst Sec RS [Assistant Secretary, Royal Society]'. 18 March 1891