Under the best conditions of atmosphere and telescope, we can see the moon's surface as it would appear at a distance varying from 800 miles to 300 miles from the earth. With a fifteen-inch telescope, under perfect conditions of vision, objects can be seen as if they were at a distance of 800 miles from the earth, and with the most powerful glasses, and the best conditions of atmosphere this distance can be reduced to about 300 miles. This would enable us to clearly see large objects like rivers, lakes, seas, or forests, if they existed, but would not be sufficient to enable us to see houses, buildings, or roads. When we come to examine the surface of the moon under the most favorable conditions, we find that it is extremely irregular. There are plenty of high mountains. These mountains are not collected in ranges as they are on the earth's surface, but are completely separated from each other, and are scattered in great numbers over the moon's surface. You may form some idea of the number of volcanoes that have been observed on the moon when I tell you that as many as 32,000 have been seen on that side of the moon that is turned towards the earth. Now it is an interesting fact that almost all these mountains possess great craters that are not unlike some of the volcanic craters we see on the earth. The volcanic craters of the moon, however, are of very much greater size than those on the earth, many being from fifty to sixty miles in diameter, while some of them are more than 100 miles in diameter. Smaller craters, say from twenty to twenty-five miles in diameter, can be counted by the hundreds. Like most of the moon's craters, the largest crater more closely resembles one of the pit-craters or calderas on the island of Hawaii. This volcanic crater consists of a huge circular ring with a small irregular peak that rises inside the ring. This peak, by the way, might at first appear to resemble the crater of Vesuvius, which after a long period of inactivity of the mountain during the eruption that destroyed Pompeii and Herculaneum was thrown up inside of what had been left standing of the old crater of Somma. But it has no crater at its summit, and, therefore, resembles rather the irregular pile or rock that rises from the surface of a lava lake in the craters of Mt. Loa or Mt. Kilauea in Hawaii. Besides the numerous craters to be seen on the moon's surface there are many lines of deep, crooked valleys, known as _rills_, that may at one time have been the beds of rivers. Besides the rills, there are many straight clefts about half a mile in width, that extend down into the surface of the moon for unknown depths. These clefts can be seen passing directly through mountains and valleys. They are believed to be cracks or fissures in the moon's surface.