1840-50] ROYAL ASTRONOMICAL SOCIETY 91 that any result of value could be derived from observations with the Cape mural circle. After Henderson's time the circle was sent back to England in 1840 to be overhauled, and to Simms' and Airy's great astonishment it turned out that the steel collar was virtually loose upon the pivot ; it had never been shrunk on, but was merely attached by soft solder. Yet Henderson undoubt- edly exhibited the parallax of a Centauri in the measures of zenith distance derived with this instrument. All his other work was equally well judged. At the time of which we write he was living at Edinburgh, but he had formerly spent frequent periods in London, and so was well known to members of Council. Amiable and unobtrusive, he was very modest about his own merits. The biographical notice of his work in 1845 February is written from personal knowledge. " The character of Mr. Henderson as an astronomer stands high, and his name will go down to posterity as an accurate observer, an industrious computer, a skilful mani- pulator, and an improver of methods in that department fo which he devoted himself. . . . Every observation is scrupulously discussed, ... his processes are fully explained, no labour is evaded, and no circumstance that can affect the accuracy of the final result is passed unnoticed. . . . One of his most distin- guishing qualities was sound judgment. He never attempted anything to which his powers were not fully equal ; and, as a consequence of this, whatever he did he did well." Hansen. In 1842 the Medal was awarded to Hansen for his new methods in planetary and lunar theory. The work had then been applied in outline to the theory of Jupiter and Saturn, and formally, to the moon in the work Disquisitio Nova. The great task of cal- culating the moon's inequalities numerically was still unperformed. It is instructive of the advanced position of gravitational astronomy at that epoch to read Lord Wrottesley's excellent address in making this award. The statement of what Hansen had aimed at and accomplished in his new theory could hardly be improved. The attitude of Hansen to the Society is also interesting. Shortly after this award he found an improvement of his method applicable to the perturbations of very eccentric and highly inclined orbits. He wrote at once to Airy, " I hasten to communicate to you a piece of astronomical intelligence of some importance," and later to Rothman, the Secretary, in similar terms. The Council registered a suitable note of thanks and congratulation on a method " which we are thus far entitled to regard as a most brilliant conquest over one of the residual difficulties of physical astronomy." The Council had not at that time any practice or unwritten law which restrained it from awarding the Medal to one of its own body. In 1843 it was awarded to Baily, on the completion of the
