Copy letter from Herbert Rix, to Senor Professor Achische F Vallin, Caballero de Graan, 14, Madrid 'Dear Sir, I am instructed by our President (Lord Kelvin) to thank you for your goodness in sending the copy of your discourse delivered before the Real Academia de Ciencias. I am, Sir, Your obedient servant, H Rix Asst. Sec. RS. [Assistant Secretary, Royal Society]'. 6 April 1894