PLATE VI. 



MOON'S AGE 14 DAYS, I HOUR. JULY IQ, l8gi. LICK OBSERVATORY. 



In this plate the moon is nearly full, the light being oblique enough to illuminate the crater 

 walls on the eastern margin alone. 



The maria are well shown nearly to the eastern margin. Separated by a belt of relatively high 

 ground from the Oceanus Procellarum is the large vulcanoid Grimaldi. It has a small crater on 

 its floor near its northern side. This vulcanoid has a floor nearly as dark as the seas. It will be 

 noted that Plato has also a dark floor. On the margin of the Oceanus Procellarum, southwest 

 of Grimaldi, is a crater Letronne, the wall of which that faces the maria is, as in other instances, 

 ruined apparently by the lava of the sea. Other like examples are shown in this neighborhood. 

 On the shores of the M. Humorum, there are three similar instances of crater-walls broken down 

 on the seaward side. 



It should be noted that none of the maria distinctly attain the margin of the moon's surface. 

 On the eastern lands the O. Procellarum comes near to the border of the moon, but high rugged 

 land is visible on the very edge. This is more clearly disclosed at certain stages of libration. 

 On the southwest border some observers think there is a sea crossing the border, but, as will be 

 seen, the level land there has not the characteristic dark hue of the maria. 



It will be observed that in this nearly vertical light, except Grimaldi and Plato, the craters on 

 the eastern margin only are distinctly visible. Those exceptions are due to the dark color of their 

 floors. There are two- or three craters near the south pole which, because they have rather dark 

 bottoms, are faintly seen. 



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