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as Mare Procellarum, the Sea of Storms; Mare Serenitatis, the Sea of Calms, etc. These names, fanciful though they be, are still retained to designate the large dark regions on the moon. A very slight improvement in the telescope, however, showed that the idea of these dark regions being oceans was an illusion. They are all covered with inequalities, proving that they must be composed of solid matter. The difference of aspect arises from the lighter or darker shade of the materials which compose the lunar surface. These are distributed over the surface of the moon in a very curious way. One of the most remarkable features are the long bright lines which radiate from certain points on the moon. A very low telescopic power will show the most remarkable of these; a good eye might even perceive it without a telescope. On the southern part of the moon's hemisphere, as we see it, is a large spot or region known as Tycho, and from this radiate a number of these bright streaks. The appearance is as if the moon had been cracked and the cracks filled up with melted white matter.

Whether we accept this view or not, it is impossible to examine the surface of the moon without the conviction that in some former age it was the seat of great volcanic activity. In the centre of all the great circular mountains we have described are craters which, it would seem, must have been those of volcanoes. Indeed, a hundred years ago it was supposed by Sir William Herschel that there was an active volcano on the moon, but it is now known that this appearance is due to the light of the earth reflected from a very bright spot on the moon's