So successful was this instrument, that he obtained a patent for it for seventeen years. In the same year an exact duplicate of this invention was brought from France, and another patent taken out for the same number of years, by Mr. William Petty,[56] who claimed to be the inventor. Wren was indignant at the notion that he had copied another person's idea, and gives good reasons for his belief that his own instrument had been described to Petty by a friend of his. Three years later Wren wrote of it as 'an obvious Thing, a cast-off Toy;' ending, 'Indeed though I care not for having a Successor in Invention, yet it behoves me to vindicate myself from the Aspersion of having a Predecessor.' Another invention Wren describes as a 'weather clock.' It consisted of a clock affixed to a weather cock that moved a rundle covered with paper, upon which the clock moved a black-lead pencil, so that the observer, by the traces of the pencil on the paper, might certainly conclude what winds had blown in his absence for twelve hours' space. The 'Parentalia' contains a careful drawing in pen and sepia of this invention elaborately worked out and remarkable for the truth and finish of the drawing. Some of these designs, and an instrument for sowing corn, nearly identical with a modern 'drill,' he dedicated in a quaintly formal letter to his father's friend, the Prince Palatine. He appeared before the Prince in another character, due probably to his Westminster training. A play was performed (about 1652) at Oxford before the Prince, Dr. Seth Ward,[57] and several others, entitled 'Hey for Honesty, down with Knavery,' translated by Thomas Randolph from the Plutus of Aristophanes, in which Christopher sustained the part of Neanias.[58] It is provoking to have this bare record merely, and no clue as to the success or failure of any part of the performance, especially where the young actor was concerned. To about the same date belongs a Latin letter written by Christopher to his father, signed 'Christophorus Regulus,' describing in glowing terms a visit paid in the spring to a friend's house. Some pretty touches give 'the lofty woods with their clamorous republic of rooks, the great fountains, the placid pools--without, you might say a terrestrial paradise, but within, heaven itself.' It may have been, though there is nothing in its favour but conjecture, that this was Bletchingdon House, and that among 'the virgins singing holy psalms,' whom he mentions, was his future bride Faith, (or as she spelt it, 'ffaith') Coghill. The letter says much, as does all that passed between them, for the warm affection existing between father and son, and the sincerely religious tone of Christopher's mind. [_BATTLE OF WORCESTER._]