Copy letter from Robert William Frederick Harrison, to the Secretary, the Society of Arts, John Street, Adelphi, W.C. 'Dear Sir, I enclose a letter, dated December 15, 1901, from Herr Rud. Custodis, dealing with the question of vision in fog, which I have been requested by the writer to forward to you. I am, Yours faithfully, Robt Harrison Asst. Sec. R. S. [Assistant Secretary, Royal Society]'. 2 January 1902