In 1661, Christopher resigned his Gresham Professorship, in order to accept the Savilian Professorship of Astronomy, at Oxford.[88] It had been held by Dr. Seth Ward, who was soon afterwards made Bishop of Salisbury in succession to Bishop Hyde. Shortly after his appointment, Christopher had a command from the King to make him a lunar globe, according to the observations made with the best telescopes. He constructed one 'representing not only the spots and various degrees of whiteness on the surface, but the hills, eminences, and cavities moulded in solid work.' This curious toy was highly admired, placed in the King's cabinet at Whitehall, and esteemed a great 'rarity.' In this year Wren took his degree as Doctor of Civil Laws, Oxford, and received a similar honour from the University of Cambridge. King Charles purposed paying a visit to Oxford, and the Philosophical Society both there and in London resolved to give him an entertainment. Lord Brouncker wrote from London to Wren to consult him. Wren wrote back:-- 'My Lord,--The Act and noise at Oxford being over, I retir'd to myself as speedily as I could to obey your Lordship and contribute something to the collection of Experiments designed by the Society, for his Majesty's Reception. I concluded on something I thought most suitable for such an occasion; but the stupidity of our artists here makes the apparatus so tedious that I foresee I shall not be able to bring it to anything within the time proposed. What in the meanwhile to suggest to your Lordship I cannot guess.'... 'Geometrical problems, and new methods, however useful, will be but tasteless in a transient show.' He enumerates various things which he had thought of and rejected: 'designs of engines, scenographical tricks, designs of architecture, chymical experiments, experiments in anatomy, which last are sordid and noisome to any but those whose desire of knowledge makes them digest it.' 'Experiments of Natural Philosophy are seldom pompous, and certainly Nature in the best of her works is apparent enough in obvious things, were they but curiously observed; and the key that opens treasures is often plain and rusty, but unless it be gilt it will make no show at Court.' He proposed to show an experiment with a 'weather wheel to measure the expansions of air.' Another--'no unpleasing spectacle--of seeing a man live without new air as long as you please;' this was to be effected by an instrument of Wren's invention which cooled, percolated, and purified the air. Also 'an artificial eye truly and dioptrically made as big as a tennis-ball.' ['_SO MUCH TATTLE._']