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Rh contributor to what is now termed Selenography. He added about sixty names to the lunar nomenclature—principally in the southwestern quadrant. He also measured the height of many of the lunar summits by an improved method, and even at the present day he is considered one of the three great authorities on this subject. He was the discoverer of those curious cracks in the Moon's surface which are known as the lunar rills, and introduced the system of designating the less important points on the Moon's surface, in the vicinity of any given formation, by means of letters from the Greek and Roman alphabets. Schroter lived to see his observatory, his library and his vmpublished ' observations wantonly destroyed by fire by the French under Vandamme in 1813. His life was wrecked, and he survived the blow but a few years.

In 1824 Lohrmann issued four sections of a map on a scale of thirty-eight inches to the Moon's diameter, which, had it been complete, would have been by far the best in existence at that time. Failing eyesight, followed by his death in 1840, delayed publication, and the remaining twenty-one sections were not issued until 1878. A small, complete map, fifteen inches in diameter, was published by him in 1838.

In 1837 appeared Beer and Madler's great work on the Moon, accompanied by a map on nearly the same scale as Lohrmann's uncompleted charts, but both more detailed and more accurate. This publication was and is still considered in some respects the standard authority on the Moon, yet the observations, chiefly due to Mädler, were all made with a telescope of less than four inches aperture. These measurements include also the heights of some 830 summits. About 150 names were added to lunar nomenclature. The work was in fact so accurate and comprehensive that it served to discourage lunar observation in other quarters, and even until within a few years its influence was shown in the very prevalent opinion that the Moon was dead and unchangeable, and so accurately charted and known that it was a waste of energy for an astronomer to devote his time to it, except to study its motions.

One astronomer, however, Schmidt, of Athens, was not discouraged, and for thirty-four years devoted himself assiduously to selenographical work, producing at the end of that time his great map of the Moon, published in 1878 by the German Government. The map consists of twenty-five sections, and is upon a scale of seventy-five inches to the Moon's diameter. This map contains upward of 32,000 craters, together with about 1,000 rills, the great majority of the latter having been detected by Schmidt himself. The heights of many summits were also determined.