Copy letter from Robert William Frederick Harrison, to A P Trotter, Electrical Standards Laboratory, Board of Trade, 8 Richmond Terrace, S.W. Lord Rayleigh's papers are brought down to 1901, and so therefore include what they want. Harrison finds in volume four is the one on the Reflection of Sound or Light from a Corrugated Surface - read to the British Association, 1893. Harrison does not notice any other. 30 November 1909