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ft, herigonius

»agatharchides humorum^'^ hippalus ¿. . 4cap'éü<elvin

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áfcpimenides inghirami wargen phoc longomontanus vcheiner ulaproth ■ casatus

tains form a ring more than 600 miles in diameter. The even more obscure book mountains mark a smaller concentric ring about 400 miles across, and the last of six such rings is the nearly circular shore of a mare plain 300 miles in diameter. Pimplelike limb markings occasionally seen west of Grimaldi are the D'Alembert Mountains. At the terminator and on the south edge of the rough region southeast of Grimaldi is a black speck marking the Sia-mese-twin craters Sirsalis and Sirsalis A.

Just north of Grimaldi is smaller but better-walled Hevelius, its light floor delicately outlined in black, and tangent to Hevelius on the north, is smaller Cavalerius, a short but strong black streak. Three of its lengths north of Hevelius we find Cardanus, a young crater similar to Cavalerius. and just north of Cardanus is its identical twin Krafft. Half bright and half dark, they appear as elongated black dots since the bright east halves are only slightly brighter than the Procellarum plain. Northeast of Krafft, nearly twice the distance to Cardanus, is the similar crater Seleucus. The rays that pass south of it, running from Cardanus toward Aristarchus beyond the terminator, still may be visible, but they are very weak. Just northwest of Seleucus is the bright wishbone—the large crater Eddington with its south wall melted away. Its west wall is also the displaced east wall of Otto Struve, which, with its large intruder Russell on the north, forms a double crater that extends twice as far north as does the wishbone. If you can resolve the long, irregular west walls of Otto Struve and Russell you will see the Hercynian Mountains, an alias by which those features are known. They have the strange property of appearing bright even when the sunset terminator is near, a property which casts some doubt on their mountainous character. With a large positive libration in longtitude, Eddington, Otto Struve, Russell, and the Hercynians are foreshortened into a single ridge close to the limb. If, in addition, there is a large negative libration in latitude, the north cusp of the crescent appears perfectly smooth and reveals none of the craters listed in the next paragraph.

The most prominent crater of the far northern continent is Pythagoras. Close to the terminator, with average libration, it has a broad bright east wall and an even broader black northwest wall. The bright central peak rises from the edge of the wall shadow and casts its own long, pointed shadow across the floor and up the east wall. On the southwest edge of Pythagoras may be seen a broad, narrow, darkened area or bite. That ij the western half of Babbage through which the terminator passes this morning. Tangent to Bah-bage on the west is smaller oenopides, 46 miles in diameter and 7200 feet deep, which at last has acquired enough wall contrast to be seen. Jmt southwest of the last crater is younger, deeper markov, 25 by 27 miles across and 8900 feet deep It appears as a black speck close to the terminj. tor.

I have pushed along swiftly this morning with little pause for description and discussion, a pro. cedure dictated by the short interval in which we are permitted to observe the moon at this advanced age. The 27-day moon is an unusual sight—a sight which most people probably never see during their entire lives.

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