“Then please reverse the photograph, for we must not lose ourselves in dreams. You will notice that the range of the lunar Apennines runs between the _Mare Vaporum_ and the _Sinus Æstuum_ on one side, and the _Mare Imbrium_ on the other. The entire chain of the Apennines is beautifully shown here. They are exceedingly steep on the side facing the _Mare Imbrium_, and gigantic peaks standing upon their long wall cast immense shadows over the ‘sea.’ Their southwestern slopes are comparatively gentle, rising gradually from the level of the _Mare Vaporum_. At their upper or southern end, in the direction of Copernicus, they suddenly terminate with a beautiful ring, which is called Eratosthenes. This is a fine example of the disk or cup shape of the lunar volcano. The bottom of Eratosthenes lies 8,000 feet below the level of the surrounding _Mare_, while peaks on its wall are as much as 15,000 or 16,000 feet in height. Between the lower end of the Apennines and the upper end of the Caucasus Mountains a strait opens a broad, level way between the _Mare Imbrium_ and the _Mare Serenitatis_. On one of the large photographs these two ‘seas’ and the strait connecting them are represented in all their picturesque details, as you will see when we come to study them. I promise you at that time a free rein to your imagination and plenty of room for its flights. On the northern border of the _Mare Imbrium_ and close to the terminator we see once more the remarkable oval valley to which I referred when pointing out the lunar Alps, and which bears the name of Plato. I call your attention to it and also, again, to Copernicus, in order that you may compare their appearance here with that which they present in the next photograph, taken when the moon’s age was eleven and three-quarter days.” [Illustration: NO. 10. NOVEMBER 30, 1903; MOON’S AGE 11.78 DAYS. ] We hereupon turned to photograph No. 10. “Now,” I continued, “observe the difference that some two days’ advance of the sunlight has produced. Plato is far within the illuminated part of the disk, and it looks darker than before. Copernicus, on the other hand, which appeared as a sharp ring with one border dark when it was near the sunrise line, has now become a round, white spot, somewhat darker in the center, with a great grayish splatter surrounding it upon the surface of the _Mare_. In the meantime, over nearly the whole extent of the _Mare Imbrium_ the sun has risen and two other _mares_ have made their appearance, one of which, extending across half the width of the eastern hemisphere, might be called the Pacific Ocean of the moon, if it had any water. It is named the _Oceanus Procellarum_, the ‘Ocean of Tempests,’ while at its southern extremity a very dark nearly circular expanse, inclosed with mountains, bears the name of the _Mare Humorum_, ‘Sea of Humors.’” “Evidently the astronomer who bestowed that name was not in a joking mood else he would surely have called it the ‘Sea of Humor.’”