About 1760, Mayer, a famous German astronomer and the director of the observatory of Göttingen, began the publication of a magnificent map of the Moon, drawn after lunar measurements all rigorously verified by himself. Unfortunately his death in 1762 interrupted a work which would have surpassed in accuracy every previous effort of the kind.
Next appears Schroeter of Erfurt (1745-1816), a fine observer (he first discovered the Lunar Rills), but a poor draughtsman: his maps are therefore of little value. Lohrman of Dresden published in 1838 an excellent map of the Moon, 15 inches in diameter, accompanied by descriptive text and several charts of particular portions on a larger scale.
But this and all other maps were thrown completely into the shade by Beer and Maedler's famous Mappa Selenographica, so often alluded to in the course of this work. This map, projected orthographically—that is, one in which all the rays proceeding from the surface to the eye are supposed to be parallel to each other—gives a reproduction of the lunar disc exactly as it appears. The representation of the mountains and plains is therefore correct only in the central portion; elsewhere, north, south, east, or west, the features, being foreshortened, are crowded together, and cannot be compared in measurement with those in the centre. It is more than three feet square; for convenient reference it is divided into four parts, each having a very full index; in short, this map is in all respects a master piece of lunar cartography.[B]
After Beer and Maedler, we should allude to Julius Schmitt's (of Athens) excellent selenographic reliefs: to Doctor Draper's, and to Father Secchi's successful application of photography to lunar representation; to De La Rue's (of London) magnificent stereographs of the Moon, to be had at every optician's; to the clear and correct map prepared by Lecouturier and Chapuis in 1860; to the many beautiful pictures of the Moon in various phases of illumination obtained by the Messrs. Bond of Harvard University; to Rutherford's (of New York) unparalleled lunar photographs; and finally to Nasmyth and Carpenter's wonderful work on the Moon, illustrated by photographs of her surface in detail, prepared from models at which they had been laboring for more than a quarter of the century.
Of all these maps, pictures, and projections, Barbican had provided himself with only two—Beer and Maedler's in German, and Lecouturier and Chapuis' in French. These he considered quite sufficient for all purposes, and certainly they considerably simplified his labors as an observer.
His best optical instruments were several excellent marine telescopes, manufactured especially under his direction. Magnifying the object a hundred times, on the surface of the Earth they would have brought the Moon to within a distance of somewhat less than 2400 miles. But at the point to which our travellers had arrived towards three o'clock in the morning, and which could hardly be more than 12 or 1300 miles from the Moon, these telescopes, ranging through a medium disturbed by no atmosphere, easily brought the lunar surface to within less than 13 miles' distance from the eyes of our adventurers.
Therefore they should now see objects in the Moon as clearly as people can see the opposite bank of a river that is about 12 miles wide.