PLATE IX. 



moon's age 2 1 DAYS, 1 6 HOURS. iSg^". 



In this plate is depicted an area from near the moon's equator to near the south pole. On 

 the eastern margin the sunlight is passing from the surface, the evening light being so oblique that 

 the bottoms of the vulcanoids are more or less in shadow. Here and there, in the advancing night, 

 there are lofty peaks on the margin of crater-rims, which still receive a touch of sun and appear 

 as bright points in a black field. On the western margin the surface is still well illuminated, with 

 the consequent effect that the surface appears to be much smoother than it is. A view taken a 

 few hours later would show about as rude a margin as is here depicted. 



Perhaps more effectively than any other this view shows how the general surface of the moon 

 outside of the maria is essentially made up of vulcanoids and ridges, the apparently smooth parts 

 appearing so only because the small irregularities are not visible. In this connection it should be 

 noted that near the dark part the surface is seen to be beset by small shallow craters, the smallest 

 visible being more than a mile in diameter, and probably several hundred feet deep. Such pits, 

 in equal numbers to the unit of surface, exist on the bright part to the left when they are observed 

 by the higher light. 



The way in which the smaller craters cut the larger is shown at many points in this field of 

 view. So, too, the relative lack of sharpness of outline of the greater vulcanoids as compared with 

 the lesser objects of this group. The low, narrow ridges which surround the pits are insufficiently 

 shown because the light does not bring them out. They are best observed near the uppermost 

 part of the picture. 



The generality of the fact that the larger craters have flat floors and that these floors are pre- 

 vailingly nearly level is well indicated. So, too, the fact that there is a prevailing tendency of 

 these floors to have either a small crater or a cone in or near the center of each circular field. 

 Four such craters in the central part of the area extending in an obscure line from near the base 

 to near the middle of the picture have cones in their centers. In all, about a dozen of the hundred 

 or so instances in which they would be recognizable have this feature. It will be evident that all 

 the craters in this region have their floors far below the level of the encircling ring, and below the 

 general lunar surface. 



In sundry instances two adjacent vulcanoids of moderate size have their neighboring walls 

 broken down so that they exhibit the first stage of " crater valleys " with a general north and south 

 axis. There are in all about ten cases of this kind on this field, but several of them are not well- 

 disclosed by this illumination. 



98 



