PLATE TTI. 



Mooii^s age, 14 days 1 hdur. Juli/ 19, 16'91. Lick Ohservatory. 



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 vuU'anoid < Irimaldi. 

 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 rather 

 indistinctly seen, 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 tliree 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, l)ut higli, rugged land is obscurely 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 nearly level area 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 Plato, the craters on 

 the eastern margin only are distinctly visiV)le. 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. 



