The peculiarities presented by a spot upon the moon are to be observed from hour to hour (or from day to day, according to the size of the spot) as the sun's light gradually sweeps across it, until the spot is fully lighted; then as the moon wanes and the sun's light gradually passes from the spot, the series of observations is to be renewed.

A comparison of them is likely--especially if the observer is a good artist and has executed several faithful delineations of the region under observation, to throw much light upon the real contour of the moon's surface at this point.
In the two lunar views in Plate 7 some of the peculiarities I have described are illustrated.

But the patient observer will easily be able to construct for himself a set of interesting views of different regions.
It may be noticed that for observation of the waning moon there is no occasion to wait for those hours in which only the waning moon is visible _during the night_.

Of course for the observation of a particular region under a particular illumination, the observer has no choice as to hour.

But for generally interesting observations of the waning moon he can wait till morning and observe by daylight.