ing observation, last September, of a remarkable change of tint from bright to sombre, and back to bright again, in the course of forty-eight hours; suggesting perhaps the formation and dissipation of cloud, perhaps the deposition and subsequent melting of hoar-frost over an area of some hundreds of square miles.
Returning to the Mare Cimmerium, we observe in the middle of it a long, lighter streak, Cimmeria, scarcely perceptible at this last opposition, and, barring its western end, the second in the procession of similarly inclined peninsulas that follow one another westward upon this side of the planet., the peninsula Hesperia, a place with a history, as will appear later on.
In the next picture (Plate. XI) Hesperia is central, dividing the Mare Cimmerium on the left from the Mare Tyrrhenum on the right. The lower end of the latter is called the Syrtis Minor, in contradistinction to the Syrtis Major, which is just appearing round the western limb. From the bay, so to speak, upon the left of Hesperia, two canals proceed down the disk in divergent directions,—the most easterly one the Aethiops, the other the Achelous. From the Syrtis Minor proceed two others, more or less similarly inclined,—the Lethes and the Amenthes.
To the west of Hesperia and parallel to it is a third cornet-tail peninsula, Lemuria, connect-
