The travellers were desirous of examining the moon during their transit, and in order to facilitate the survey of this new world they took an excellent map by Boeer and Moedler, the Mappa Selenographica, published in four plates, which is justly looked upon as a masterpiece of patience and observation.
Boeer and Moedler composed their celebrated Mappa Selenographica, according to an orthographical projection.
Some of the large craters present the same appearance. Barbicane knew this opinion of the German selenographer, an opinion shared by Boeer and Moedler. Observation has proved that right was on their side, and not on that of some astronomers who admit the existence of only gray on the moon's surface.
Galileo used it, and since Messrs. Boeer and Moedler have employed it with the greatest success. Another method, called the tangent radii, may also be used for measuring lunar reliefs. It is applied at the moment when the mountains form luminous points on the line of separation between light and darkness which shine on the dark part of the disc.
But Herschel was mistaken too, and the observations of Schroeter, Louville, Halley, Nasmyth, Bianchini, Pastorff, Lohrman, Gruithuysen, and especially the patient studies of MM. Boeer and Moedler, were necessary to definitely resolve the question. Thanks to these savants, the elevation of the mountains of the moon is now perfectly known.
The earliest observations did not discover these furrows. Neither Hevelius, Cassini, La Hire, nor Herschel seems to have known them. It was Schroeter who in 1789 first attracted the attention of savants to them. Others followed who studied them, such as Pastorff, Gruithuysen, Boeer, and Moedler.
But Herschel's calculations were in their turn corrected by the observations of Halley, Nasmyth, Bianchini, Gruithuysen, and others; but it was reserved for the labors of Boeer and Maedler finally to solve the question. They succeeded in measuring 1,905 different elevations, of which six exceed 15,000 feet, and twenty-two exceed 14,400 feet.
Boeer and Moedler measured 1,905 different elevations, of which six exceed 15,000 feet and twenty-two exceed 14,400 feet. Their highest summit towers to a height of 22,606 feet above the surface of the lunar disc. At the same time the survey of the moon was being completed; she appeared riddled with craters, and her essentially volcanic nature was affirmed by each observation.
With the help of Boeer and Moedler's Mappa Selenographica, the travelers were able at once to recognize that portion of the disc enclosed within the field of their glasses. "What are we looking at, at this moment?" asked Michel. "At the northern part of the `Sea of Clouds," answered Barbicane. "We are too far off to recognize its nature.
The travelers being desirous of examing the moon carefully during their voyage, in order to facilitate their studies, they took with them Boeer and Moeller's excellent Mappa Selenographica, a masterpiece of patience and observation, which they hoped would enable them to identify those physical features in the moon, with which they were acquainted.