But the greater part of Wren's declining years was spent at Hampton Court, from which he went up to London to watch the progress of the works at Westminster Abbey, the surveyorship of which he still kept. A report was spread that the ceiling of the Sheldonian Theatre, in which, as a piece of mechanical construction, Sir Christopher took great pride, was giving way. Careful examination proved this to be a perfectly groundless rumour, and no further annoyance arose to disturb the calm evening of the old man's life. To be 'beneficus humano generi,' as he said, had ever been his aim and wish. He now employed his leisure in looking over old papers on astronomy and mathematics and the method of finding out the longitude at sea. It had been long considered by the general world as impossible to find out as was the secret of perpetual motion, and the attempt at either discovery was treated with equal ridicule. The merchants, and captains of merchant ships were, however, from bitter experience of vessels and crews wrecked or lost, aware of the immense importance of the discovery of the longitude, if it could be made. They presented, in 1714, a petition to Parliament, begging that a reward might be offered 'for such as shall discover the same.' This, after due consideration, was done by a Bill, passed rapidly through both Houses, offering a reward of 20,000_l._. for the discovery.[245] The subject was one which greatly occupied Wren, who all his life had been interested in sailors and sea matters. He amused himself by throwing his latest thoughts on the longitude into the form of three cryptographs:[246] 1. OZVCVAYINIXDNCVOCWEDCNMALNABECIRTEWNGRAMHHCCAW. 2. ZEIYEINOIEBIVTXESCIOCPSDEDMNANHSEFPRPIWHDRAEHHXCIF. 3. EZKAVEBIMOXRFCSLCEEDHWMGNNIVEOMREWWERRCSHEPCIP. A copy, signed by Halley as a true one, of this cipher was sent to the Royal Society in 1714 by Wren's son. Probably Sir Christopher had not perfected his instruments sufficiently to proclaim his discovery, and did not wish either to lose his idea, or, when later on he disclosed it, to appear as a plagiarist in case a similar method had suggested itself to anyone else. Old age had weakened Wren's limbs, but had had little effect on his clear understanding; his scientific pursuits interested him still, and were among the employments of those few leisure years which closed a life of incessant work. He gave, however, the greater part of his time and care to the diligent study of the Holy Scriptures, which all his life he had loved; and thus, serene and gentle as ever, waited for his summons. [_HIS DEATH._]