Plate showing a view of Mare Humorum, a lunar basaltic plain formed by ancient volcanic eruptions. It is described as follows by the author:
The “Mare Humorum,” or sea of moisture, as it is called, which is represented on plate VI., is one of the smaller gray lunar plains. Its diameter, which is very nearly the same in all directions, is about 270 miles, the total area of this plain being about 50,000 square miles. It is one of the most distinct plains of the moon, and is easily seen with the naked eye on the left-hand side of the disk. The floor of the plain is, like that of the other gray plains, traversed by several systems of very extended but low hills and ridges, while small craters are disseminated upon its surface.