Copy letter from Christian Huygens, Paris, to Henry Oldenburg 'Concerns the conformity of his rules of Motion to those of Dr Wren, and a way of securing Philosophical discoveryes to their authors Note at end: 'Dr Wren at ye same meeting of the Royal Society gabe the following Anagram for a Secret of his Invention, which was returned to Monsieur Hugens; viz q b c d e f g h i l m n o p r s t u x y 7 4 4 4 12 1 3 6 10 7 1 7 9 2 6 2 7 4 1 1' 6 February 1669