it, and there remain only the small ones which occasionally cross its path. These are called "Leonids" or "Lyrids" or "Perseids," and these meteor showers occur at nearly the same time every year when the earth runs through a swarm of them on its pathway round the Sun. But they are very small. Some of them are no bigger than a slate pencil. Few are as big as brickbats, and nearly all are burnt up by the air-friction before they reach the earth's surface. Larger ones still fall on the earth, however, and it is calculated that many hundreds reach us in fragments every year. But when the earth was young many thousands fell every day. To this era, or immediately before it, belongs the birth of the Moon. It is a subject of interest to geologists, because it is admitted that the materials of which the Moon is constituted are similar to those of the earth; and it is believed that its history up to a certain point was very like that of the earth. It had its great volcanic era such as we have described; but its development closed shortly afterwards. We are considering, however, at this moment its origin. It was once part of the earth. All of us have read of those little animals, of which one form is the amœba and another form the white corpuscles of the blood. If we watch them under the microscope we may see one of them slowly lengthen out, then break in two, and each part go swimming away by itself, a perfect animal. It was Sir G. H. Darwin, F.R.S., who proved mathematically in 1879 that the origin of the Moon was such that we may properly compare it to the splitting up of the little animals just described. The date of this event cannot be fixed even approximately--beyond saying that as astronomical events go it must have been rather recent, though not less than fifty million years ago. The Moon is therefore one of the younger members of the Solar System. But no other catastrophe, either before or since, has occurred on the earth to compare with its prodigious birth. Five thousand million cubic miles of material left the earth's surface never again to return to it. Whether it all left at once or whether the action was prolonged we do not know, but we may try in vain to imagine the awful uproar and fearful volcanic phenomena exhibited when a planet was cleft in twain and a new moon was born into the Solar System.