But if vegetation took the same forms on the Moon as on the Earth, and passed through the same changes, we should have no difficulty in perceiving the evidence of its presence. If we were transported to the Moon and turned our eyes earthward, we should not need the assistance of any telescope in order to detect terrestrial changes which would be plainly connected with the seasonal changes of vegetation. The Earth would present to us a disc four times the apparent diameter of the Moon, and on that disc Canada would offer as great an area as the whole of the Moon does to us. We could easily follow with the naked eye the change from the glittering whiteness of the aspect of Canada when snow-covered in winter, to the brown, green and gold which would succeed each other during the brighter months of the year. And this type of change would alternate between the northern and southern hemispheres, for the winter of Canada is the summer of the Argentine, and conversely.
We ought, therefore, to have no difficulty in observing seasonal changes on the Moon, if such take place. But nothing of the kind has ever been remarked; no changes sufficiently pronounced for us to be sure of them are ever witnessed. Here and there some slight mutations have been suspected, nearly all accomplishing their cycle in the course of a lunar day; so that it is difficult to separate them from changes purely apparent, brought about by the change in the incidence of the illumination.
The difference in appearance of a given area on the Moon when viewed under a low Sun and when the Sun is on the meridian is very striking. In the first case everything is in the boldest relief; the shadows are long and intensely black; the whole area under examination in the telescope seems as if it might be handled. Under the high Sun, the contrasts are gone; the scenery appears flat, many of the large conspicuous markings are only recognized with difficulty. Thus the terse remark of Mädler, "The full Moon knows no Maginus," has become a proverb amongst selenographers; yet Maginus is a fine walled plain some eighty miles in diameter, and its rampart attains a height in parts of 14,000 feet. Maginus lies near Tycho, which has been well named "the lunar metropolis," for from it radiates the principal system of bright streaks conspicuous on the full Moon. These white streaks appear when the shadows have vanished or are growing short; they are not seen under a low Sun.