It is somewhat remarkable that the one celestial body which Herschel neglected was our satellite, the Moon; and it is also remarkable that the Moon was for many years the chief object of study of his contemporary astronomer, Johann Hieronymus SchrÖter (1745-1816). Born at Erfurt, near Hanover, on August 30, 1745, Johann Hieronymus SchrÖter was originally intended for the study of law, for which he was sent to the University of GÖttingen. At the same time he studied mathematics, and particularly astronomy, under the mathematician, Kaestner of GÖttingen. Deeply interested in music, he became acquainted with the Herschel family, and, inspired by William Herschel’s example, determined to study the heavens. In 1779 he became the possessor of a small achromatic refractor, and commenced to observe the Sun and Moon. In 1778 he entered the legal profession at Hanover, and four years later he was appointed “oberamtmann” or Chief Magistrate of Lilienthal—“the Vale of Lilies”—in the Duchy of Bremen. At Lilienthal SchrÖter erected a small observatory, and acquired in 1785 one of Herschel’s 7-foot reflectors. In 1792 the astronomer superintended the construction of a 13-foot reflector, made by Schrader of Kiel, who transferred his workshop to Lilienthal. With these instruments the great work of SchrÖter was accomplished.

SchrÖter directed his powers of observation to the study of the Moon. He originated the study of the surface of the Moon, and founded the branch of astronomy known as selenography, or the study of the Moon’s surface. The foundations of this branch were laid in 1791 with the publication of SchrÖter’s ‘Seleno-topographische Fragmente’. The astronomer determined to make a comparative study of the surface of our satellite, and before 1801 discovered eleven “rills” or clefts on the Moon’s surface, and recognised a large number of craters. He likewise believed that he had seen a lunar atmosphere, an observation of which was made by him in February 1792. SchrÖter seems never to have doubted what Herschel and his contemporaries believed—that the Moon was a living world with volcanoes in active eruption, surrounded by an atmosphere, and inhabited by beings like ourselves. Unfortunately, SchrÖter was not good at making drawings of what he saw; nevertheless, he accomplished a vast amount of work. In the little observatory at Lilienthal the foundations were laid of the comparative study of the surface of the Moon.

But these observations were destined to be rudely interrupted. In 1810 Hanover was occupied by the invading troops of Napoleon, and SchrÖter lost his appointment as Chief Magistrate of Lilienthal, and also his income. But there was worse to follow. On April 20, 1813, three years after, the French, under Vandamme, with that cruelty which seems to belong to warfare, occupied Lilienthal, and set fire to the little village. A few days later the French soldiers entered the observatory and burned it to the ground. All SchrÖter’s precious observations, accumulated after thirty-four years’ labour, were destroyed with a few exceptions, the observations on Mars narrowly escaping the conflagration. Unable to forget the destruction of his observatory, and without the means to repair the loss, he lived only three years after the disaster. He died on August 29, 1816, “leaving behind him,” says Mr Arthur Mee, “an imperishable record, and a noble example to observers of all time.”

Wilhelm Gotthelf Lohrmann, a land-surveyor of Dresden, continued the observations of SchrÖter, and in 1824 published four of the twenty-five proposed sections of a large lunar chart. In 1827, however, his sight began to fail, and he was obliged to abandon his intention. But a successor had already appeared on the scene. Johann Heinrich von MÄdler (1794-1874) was born in Berlin in 1794, and, after a severe struggle to earn a living, entered the University of Berlin in 1817. In 1824 he became acquainted with Wilhelm Beer (1797-1850), a wealthy banker, who had come to him for instruction in astronomy, and who erected in 1829 an observatory near his villa in Berlin, where pupil and tutor pursued their studies.

In 1830 MÄdler, with Beer’s assistance, commenced a great trigonometrical survey of the surface of the Moon. The observations of Beer and MÄdler were made with no larger instrument than a 3¾-inch refractor. They ascertained the positions of 919 lunar spots, and measured the height of 1095 mountains. Their great chart of the Moon—which was afterwards followed by a smaller one—was issued in four parts during 1834-36. “The amount of detail,” wrote Proctor, “is remarkable, and the labour actually bestowed upon the work will appear incredible.” The chart has neither been revised nor superseded, and it remains to this day one of the standard works on the subject.

The chart was succeeded in 1837 by a descriptive volume entitled ‘Der Mond.’ In this work Beer and MÄdler did much for the progress of lunar astronomy. Their observations led to a change of opinion regarding our satellite’s physical condition. Herschel, SchrÖter, Olbers, and other astronomers seem to have considered the Moon a living world. MÄdler declared that it was a dead world. He believed it to be destitute of life of any kind, and the changes observed by SchrÖter and other observers were put down as illusions. ‘Der Mond’ was the end of MÄdler’s work in lunar astronomy, for, receiving an appointment at Dorpat, he went there in 1846, and retained his post until within a few years of his death, which took place at Hanover on March 14, 1874.

MÄdler’s successor in the field of lunar astronomy was Johann Friedrich Julius Schmidt (1825-1884), who was born at Eutin in LÜbeck in 1825. At a very early age he gave indications of a taste for astronomy. Fortunately his father possessed a small hand telescope, with which young Schmidt commenced his lunar studies. Appointed assistant at Bonn and OlmÜtz and director at Athens successively, he kept up his persistent study of the surface of the Moon for over forty years. In 1839, when fourteen years of age, he began the valuable series of observations which were destined to form the basis of his great chart of the surface of the Moon. Between 1853 and 1858, when employed at OlmÜtz, Schmidt made and calculated no fewer than 4000 micrometrical measures of the altitudes of lunar mountains. Before 1866 Schmidt had found no fewer than 278 “rills,” and his discoveries were the means of augmenting the number of these curious objects to nearly a thousand.

In a word, it may be said that Schmidt drew out a lunar geography, and the result of his labours, together with those of SchrÖter and MÄdler, is that in a sense we now know the features of the Moon better than those of the Earth. For instance, astronomers see the whole surface of the Moon spread before their eyes, while geographers can never have a similar view of the terrestrial features: we have never seen the poles of the Earth, while the lunar poles are well known to astronomers. For twenty years after his appointment at Athens, Schmidt worked at fixing the positions of lunar objects, measuring the heights of mountains and the depths of craters. An idea of his enthusiasm in constructing his great chart may be gained from the fact that he made almost a thousand original sketches.

MÄdler’s dogmatic assertion that the Moon was entirely a dead world was generally believed until Schmidt made observations to the contrary. From 1837 to 1866 the popular opinion was that our satellite was an absolutely dead world. Consequently there was little progress in lunar astronomy during those thirty years. Although MÄdler’s view was much nearer the truth than the opinions of his predecessors, it was also too positive. His confident assertion, which was received without hesitation, was never questioned until Schmidt came upon the scene. To Schmidt the Moon was not entirely dead, and it was he who brought forward indisputable evidence as to the existence of changes on its surface. In October 1866 he announced that the crater LinnÉ had lost all appearance of such, and that it had become entirely effaced. Lohrmann and MÄdler had observed it under a totally different aspect, as also had Schmidt himself from 1840 to 1843. There was great excitement in the astronomical world on Schmidt’s announcement, and many astronomers denied the change, although Schmidt’s observation was confirmed by Secchi and Webb. The evidence in favour of it preponderated, and very few observers now consider the Moon’s surface to be absolutely changeless.

In 1865 Schmidt had begun to arrange his observations on the Moon into the form of a chart. At first he decided to have a chart of six feet diameter, divided, like that of MÄdler, into four sections. But in April 1868, on making an estimate of the value of such a chart, he was dissatisfied, and determined to construct a map of the same size divided into twenty-five sections instead of four. He began the work in 1868, and after six years the great map was completed. After some delay the German Government undertook to issue the chart at their expense, and it was published in 1879, after fourteen years of preparation. It contained no fewer than 30,000 objects, and its completed diameter was six feet three inches—more than double the size of any previous map of the Moon. Indeed, it was probably the greatest contribution ever made to lunar astronomy. Schmidt lived only a few years after the publication of his great chart. He died at Athens, in his fifty-ninth year, February 8, 1884.

Schmidt’s announcement of the change in the appearance of LinnÉ was followed in 1878 by a statement by Hermann Joseph Klein (born 1842) of Cologne, to the effect that a new crater had been formed to the north of the well-known lunar crater, Hyginus. The change in this case, however, is by no means so certain as in that of LinnÉ. It will be observed that the majority of the students of the Moon were Germans. In England the study was not taken up until 1864, when a Lunar Committee of the British Association was appointed. Some good lunar work was done by the well-known astronomer, Thomas William Webb (1807-1885), while the study was popularised by James Nasmyth (1808-1890), the famous engineer, who published, in 1874, in conjunction with James Carpenter of Greenwich Observatory, a beautifully-illustrated volume entitled ‘The Moon.’ This was succeeded, in 1876, by the larger work of Edmund Neison (now Nevill), Government Astronomer of Natal. About this time several English astronomers, devoted to the study of the Moon, formed themselves into the Selenographical Society. After a few years, however, the society came to an end, and the enthusiasts formed themselves into the lunar section of the British Astronomical Association, on the foundation of that society in 1890. Chief among those English selenographers was Thomas Gwyn Elger (1837-1897), whose observations of the Moon and drawings of the various craters were of the utmost value. Two years before his death, in 1895, Elger published his important work, ‘The Moon,’ along with an exhaustive chart of the visible face of our satellite.

Herschel and SchrÖter firmly believed in the existence of a lunar atmosphere, the latter believing that he had actually observed the Moon’s atmospheric envelope. Early in the nineteenth century it was soon observed, however, that on the Moon passing over and occulting stars, these stars disappeared suddenly behind the Moon’s limb, instead of gradually, as they should have done, had an atmosphere of any density existed. Accordingly astronomers gave up believing in a lunar atmosphere. On January 4, 1865, Huggins observed with his spectroscope the occultation of a small star in Pisces. There was not the slightest sign of absorption in a lunar atmosphere; the entire spectrum vanished at once.