Copy letter from Robert William Frederick Harrison to E N de C Andrade, Physikalische Institut, Heidelberg, Germany 'I beg to acknowledge the receipt of your letter of April 29th: and in accordance with your request [herewitho] send you the diagrams illustrating your paper on the "Distribution of Slide". Please return all of them with you amended paper, marking those which you wish to be omitted.' [no enclosure] 2 May 1911