Such are the main objects of interest upon the visible hemisphere of our satellite. In observing them, the beginner will do well, after the inevitable preliminary debauch of moon-gazing, during which he may be permitted to range over the whole surface and observe anything and everything, not to attempt an attack on too wide a field. Let him rather confine his energies to the detailed study of one or two particular formations, and to the delineation of all their features within reach of his instrument under all aspects and illuminations. By so doing he will learn more of the actual condition of the lunar surface than by any amount of general and haphazard observation; and may, indeed, render valuable service to the study of the moon. Neither let him think that observations made with a small telescope are now of no account, in view of the number of large instruments employed, and of the great photographic atlases which are at present being constructed. It has to be remembered that the famous map of Beer and Mädler was the result of observations made with a 3-3/4-inch telescope, and that Lohrmann used an instrument of only 4-4/5 inches, and sometimes one of 3-1/4. Anyone who has seen the maps of these observers will not fail to have a profound respect for the work that can be done with very moderate means. Nor have even the beautiful photographs of the Paris, Lick, and Yerkes Observatories superseded as yet the work of the human eye and hand. The best of the Yerkes photographs, taken with a 40-inch refractor, are said to show detail 'sufficiently minute to tax the powers of a 6-inch telescope.' But this can be said only of a very few photographs; and, generally speaking, a good 3-inch glass will show more detail than can be seen on any but a few exceptionally good negatives. In conducting his observations, the student should be careful to outline his drawing on such a scale as will permit of the easy inclusion of all the details which he can see, otherwise the sketch will speedily become so crowded as to be indistinct and valueless. A scale of 1 inch to about 20 miles, corresponding roughly to 100 inches to the moon's diameter, will be found none too large in the case of formations where much detail has to be inserted--that is to say, in the case of the vast majority of lunar objects. Further, only such a moderate amount of surface should be selected for representation as can be carefully and accurately sketched in a period of not much over an hour at most; for, though the lunar day is so much longer than our own, yet the changes in aspect of the various formations due to the increasing or diminishing height of the sun become very apparent if observation be prolonged unduly; and thus different portions of the sketch represent different angles of illumination, and the finished drawing, though true in each separate detail, will be untrue as a whole.