Letter from Carrie Gold to Ms Susan le Roux, Art Editor, Oxford University Press, Ely House, 37 Dover street, London, W1X 4AH, England Granting permission to use figure 2 from the article in Nature 221, 25, 1969. Asks that Gold be shown the text of the figure as it appears in Lovell's book, if that is possible. 13 March 1973