Lunar photography as exemplified by the marvellous and beautiful pictures produced at the Lick Observatory under the auspices of Dr. Holden, and the exquisite enlargements of them by Dr. Weinek of Prague; at Paris by the brothers Henry; and at Brussels by M. Prinz; point to the not far distant time when we shall possess complete photographic maps on a large scale of the whole visible disc under various phases of illumination, which will be of inestimable value as topographical charts. When this is accomplished, the observer will have at his command faithful representations of any formation, or of any given region he may require, to utilise for the study of the smaller details by direct observation. Desultory and objectless drawings and notes have hitherto been more or less characteristic of the work done, even by those who have given more than ordinary attention to the moon. Though these, if duly recorded, are valuable as illustrating the physical structure, the estimated brightness under various phases, and other peculiarities of lunar features, they do not materially forward investigations relating to the discovery of present lunar activity or to the detection of actual change. It is reiterated _ad nauseam_ in many popular books that the moon is a changeless world, and it is implied that, having attained a state when no further manifestations of internal or external forces are possible, it revolves round the earth in the condition, for the most part, of a globular mass of vesicular lava or slag, possessing no interest except as a notable example of a "burnt-out planet." In answer to these dogmatic assertions, it may be said that, notwithstanding the multiplication of monographs and photographs, the knowledge we possess, even of the larger and more prominent objects, is far too slight to justify us in maintaining that changes, which on earth we should use a strong adjective to describe, have not taken place in connection with some of them in recent years. Would the most assiduous observer assert that his knowledge of any one of the great formations, in the south-west quadrant, for example, is so complete that, if a chasm as big as the Val del Bove was blown out from its flanks, or formed by a landslip, he would detect the change in the appearance of an area (some three miles by four) thus brought about, unless he had previously made a very prolonged and exhaustive study of the object? Or, again, among formations of a different class, the craters and crater-cones; might not objects as large as Monte Nuovo or Jorullo come into existence in many regions without any one being the wiser? It would certainly have needed a persistent lunar astronomer, and one furnished with a very perfect telescope, to have noted the changes that have occurred within the old crater-ring of Somma or among the Santorin group during the past thirty years, or even to have detected the effects resulting from the great catastrophe in A.D. 79, at