_Dr. Doberck’s Hints._—Dr. Doberck has given some useful hints in connection with this subject:—“In order to be as sure as possible of ultimate success it is not enough to sweep with the instrument and watch any suspicious object for proper motion. It is better to procure a large map such as Argelander’s, and, comparing the image seen in the comet-seeker with the map, to insert all the nebulous objects according as they are discovered. At the end of the watch they are then compared with the catalogues of nebulæ and clusters of stars. A general catalogue facilitates this, but is never quite sufficient, as there seems to be no limit to the number of objects in the sky, and more are constantly being catalogued. In the course of time an observer learns to remember the objects he has seen before in the seeker, and at last he need not consult the map at all. The subsequent observation of a newly-found comet is best made with the ring-micrometer if the telescope is not equatoreally mounted. In the latter case it should be made by aid of a steel-bar micrometer. As soon as three observations are available the first approximation to a parabolic orbit can generally be determined: the calculation of which is quite elementary, and would be enjoyed by many amateur astronomers who are fond of figures and would easily get used to Olbers’s method. Only the three positions must not be so near each other as to lie on a great circle.” _Prizes for Discoveries._—The Vienna Academy of Sciences formerly gave a gold medal to the discoverer of every new comet. These presentations were discontinued in about 1880; and Mr. H. H. Warner then offered a prize of $200 for every unexpected comet found in the United States or in Canada. This prize was continued in subsequent years, and the conditions were amended so as to include observers in Europe. Many of these prizes were gained by Barnard and Brooks; but they have not been re-offered during the past year or two. Mr. Warner, however, contemplates renewing them. The Astronomical Society of the Pacific now awards a bronze medal to all such discoverers. FOOTNOTES: [41] Donati’s Comet of 1858 and Coggia’s Comet of 1874 may be mentioned as good examples of the gradual approach and development of these visitors witnessed by means of the telescope. [42] It ought, perhaps, in the present state of our knowledge, to be termed “the Neptune of comets;” for it has the longest period of any comet whose path has been definitely ascertained by multiple returns to perihelion. [43] Encke’s Comet has the shortest period of all the known comets.