At the very urgent request of the late Dr Sang, who regarded the above paper as one of his chief contributions to science, I brought before the Council of the Society the question of its publication. From the Minute-Book of the Ordinary Meetings, I find that it was read on the 20th February 1837, though it is not mentioned in the published Proceedings of that date. On 21st July 1891 the Council finally resolved that the paper should be printed in the Proceedings “if otherwise found desirable.” The reasons in favour of printing it seem to outweigh those which may, readily enough, be raised against such a course.