Maury’s first volume of astronomical observations, the first indeed to be issued from an American observatory, appeared in 1846. Though this was pioneer work, it was important enough to cause one of the most distinguished astronomers of Europe to conclude that it had placed the American observatory in the front rank with the oldest and best institutions of the kind in Europe. In the appendix to this volume, Maury gives very generous credit and praise to his helpers, among whom were at this time the distinguished mathematicians Hubbard, Keith, and Coffin; but he adds that he considers himself alone responsible for the accuracy of the work as nothing had been published until it had passed his supervision and approval. A very ambitious work which Maury began during the year 1845 was a catalogue of the stars. The aim was to cover every point of space in the visible heavens with telescopes, get the position of every star, cluster, and nebula, and record both magnitude and color, with the angle of position and the distance of binary stars together with descriptions and drawings of all clusters and nebulæ. No astronomical work on such an extensive scale had ever before been executed or even attempted, though the value and importance of it were manifold and difficult of full estimation. Maury wrote that it was his intention to make a contribution to astronomy that would be worthy of the nation and the age, and to so execute the undertaking that future astronomers would value it so highly as to say that such a star was not visible in the heavens at the date of the Washington Catalogue because it is not recorded therein. An interesting example of the extremely practical value of such a catalogue came up in connection with Leverrier’s discovery of the planet Neptune. In the autumn of 1846, after the discovery of this planet, Maury ordered one of his observers to trace its path backwards to see if some astronomer had observed it and entered it as a fixed star. On February 1, 1847, the observer, Sears Cook Walker, gave a list of fourteen stars from Lalande’s catalogue in his “Histoire Céleste”, where Neptune should have been approximately in May, 1795. Professor Hubbard was then directed by Maury to examine with the equatorial, and he found on the night of February 4 that the suspected star was missing. It was concluded, therefore, that Lalande had observed and recorded Neptune as a fixed star on the nights of May 8 and 10, 1795. This discovery enabled astronomers to compute the new planet’s orbit from observations extending over a period of fifty years.