Hooke's bills of expenditure by him on the Society's account, and an order dated 23 December 1681 by Sir Christopher Wren to Abraham Hill, Treasurer, to pay Hooke £40 Expenditure on such experiments as "The Apparatus about the expt. of seeing into two objects at once" and "...the expt. of staining marble" and such domestic arrangements as "coles for the repository". 23 December 1681